UPSB v4
Off-topic / strat's Homework Help Thread
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Date: Sun, Jan 23 2011 02:37:47
Hey a lot of people have been tagging me and asking for homework help and stuff I don't mind helping but here are a few rules:
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[*]I'll never just give you the answer, first i'll show you how to go about doing it, if you still need help i'll give step-by-step for you
[*]Always mention me in your post so I see it faster
[*]I'll help if I know how to, but if I don't then sorry there's nothing i can do, I'm not going to look up how to do your homework or whatever
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Date: Sun, Jan 23 2011 03:15:20
should rename to Ask Strat :p Keep the trend going.
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Date: Sun, Jan 23 2011 04:29:55
shoeman6 wrote: @strat1227; A 2.0 kg block oscillates up and down on a spring with spring constant 210N/m . Its initial amplitude is 14 cm. If the time constant for damping of the oscillation is 4.0s , how much mechanical energy has been dissipated from the block-spring system after 12 s? |deltaE|= ____ J
Okay so i know time constant is when it is 1/e which is about .36 how do I apply that to 12 seconds, multiply the ratio by 3?... errr find the total energy, and then the energy of it at 12s using the amplitude at the time (found using the time constant)?.... /has a headache... -
Date: Sun, Jan 23 2011 04:36:57
@shoeman6 you know that after the time constant the amplitude is .36 of original, so you do (original amp)*.36*.36*.36 since 12 seconds is 3 4-second periods. then you have the new amplitude energy is found using 1/2 kx^2
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Date: Sun, Jan 23 2011 04:54:26
.14 x .36 x .36 x .36 = 0.00653184 .5x210x.14^2=2.058 .5x210x0.00653184^2=1.911E-7 ^ is that right?.... seems like a REALLLY small number... would it be 2.058-1.911E-7 = energy lost?... @strat1227;
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Date: Sun, Jan 23 2011 04:56:22
if i'm understanding the question correctly the point is to show you that after that long the spring is basically stopped moving, amplitude like 6 mm, basically not moving so the energy lost is all of it i'd check this with other classmates/teacher though, but thats what it looks like to me @shoeman6
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Date: Mon, Jan 24 2011 03:34:27
@strat1227 i have a math exam tomorrow. I have only been working a final assignment given by the teacher which covers most of the things in the exam. I have like 3 hours tomorrow to study and finish that assignment. I know this is not really asking for help, but do you think i will be okay ? O____O
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Date: Mon, Jan 24 2011 03:54:56
TheAafg wrote: @strat1227 i have a math exam tomorrow. I have only been working a final assignment given by the teacher which covers most of the things in the exam. I have like 3 hours tomorrow to study and finish that assignment. I know this is not really asking for help, but do you think i will be okay ? O____O
get off upsb now and start studying -
Date: Mon, Jan 24 2011 15:16:34
SJ wrote: get off upsb now and start studying
lol this. -
Date: Tue, Jan 25 2011 01:05:28
HEY STRAT DOES LIGHT HAVE MASS? BECAUSE LIKE, IT DOESN'T, BUT LIKE, IT ALSO DOES HAVE, LIKE, SOME OF THE, LIKE, DEFINITIONS OF MASS AT LIKE, THE SAME TIME.
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Date: Tue, Jan 25 2011 02:19:59
haha the definition of mass is coupled to the higgs boson, so no it doesn't have any of the definitions of mass :P btw i learned exactly why massive objects can bend light the other day in class, i can explain it to you better next time you ask (i think it was you i was talking to about this once before lol) @Loanshark
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Date: Tue, Jan 25 2011 03:11:30
Bu-bu-but, light has momentum, and you need mass to have momentum D: Well, black holes definitely bend light. Knowing that, I can kinda guess how other massive objects bend light too. Unless, they're somehow completely different in principle. @strat1227
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Date: Tue, Jan 25 2011 03:22:53
@Loanshark, Pretty sure we talked a bout this in chemistry, from what I learned which idk if it's true or not, but light travels in a "straight path" and gravity, or things such as black holes that are really really really massive bend space, and thus it appears as though light is being bent as well... And light has energy, which can be "made "into mass, but itself isn't massive since it's never still/// Idk maybe this view about gravity is outdated, but I remember a show where carl sagan explained very basically how space time works using a planar model, and basically having gravity as like wells in this plane, so time going straight would appear curved, and things like blackholes would just be so "steep" it would appear as though light was bent around it, when in fact space is... Strat, teach us =D
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Date: Tue, Jan 25 2011 14:39:29
@shoeman6 wow you were actually pretty close to being dead on Mass distorts "spacetime", like the way you were talking about wells in the spacetime plane Light travels in a way that is the shortest possible distance in this spacetime plane, so in the regular 3d plane it looks like it's bending but it's actually just going straight in spacetime whereas mass actually bends in spacetime (due to gravity) So if you shoot a proton and a photon side-by-side near a planet or a black hole or something, the photon will "bend", but the proton bends much more (because gravity is affecting it, but not the photon)
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Date: Tue, Jan 25 2011 22:53:46
A bit of a tangent, but why does light slow down in different mediums? Just kinda thought of it cuz like I remember seeing some theorem or something that light will refract as if it is taking the most efficient route or something. (I forget the name and what it actually said >_<)
strat1227 wrote: @shoeman6 wow you were actually pretty close to being dead on Mass distorts "spacetime", like the way you were talking about wells in the spacetime plane Light travels in a way that is the shortest possible distance in this spacetime plane, so in the regular 3d plane it looks like it's bending but it's actually just going straight in spacetime whereas mass actually bends in spacetime (due to gravity) So if you shoot a proton and a photon side-by-side near a planet or a black hole or something, the photon will "bend", but the proton bends much more (because gravity is affecting it, but not the photon)
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Date: Tue, Jan 25 2011 23:19:12
Awesome wrote: A bit of a tangent, but why does light slow down in different mediums? Just kinda thought of it cuz like I remember seeing some theorem or something that light will refract as if it is taking the most efficient route or something. (I forget the name and what it actually said >_<)
I'm pretty sure because it cannot take a direct path through. For example: -------------------------------------- >>> light in a vacuum ----/------------------------- Light would be bent by passing through the material and therefore slow down. And the more the material affects lights' ability to go in a straight line, the more the slowing of it. -
Date: Wed, Jan 26 2011 02:02:00
As I understand, strat also is working toward a math degree. Help me out! I've got this one review problem that I'm completely stumped on. Tim paid $200 to have his lawn fertilized. The lawn-care company charged $.25 per square foot. If Tim's lawn is a rectangle with a length that is twice its width, find the dimensions of the lawn. I understand that there are a total of 800 square feet in the rectangle in which l=2w, and that's about as far as I've gotten. I'd like to avoid guess and check if possible. :)
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Date: Wed, Jan 26 2011 02:09:13
nateiskewl wrote: As I understand, strat also is working toward a math degree. Help me out! I've got this one review problem that I'm completely stumped on. Tim paid $200 to have his lawn fertilized. The lawn-care company charged $.25 per square foot. If Tim's lawn is a rectangle with a length that is twice its width, find the dimensions of the lawn. I understand that there are a total of 800 square feet in the rectangle in which l=2w, and that's about as far as I've gotten. I'd like to avoid guess and check if possible. :)
The area of the lawn is y=x(2x) where x is the width, so P(x) = .25(x(2x)) is the amount of money he will pay for it. Set it equal to 200 because you know that's what he actually paid and solve for x. -
Date: Wed, Jan 26 2011 02:24:20
AwonW wrote: The area of the lawn is y=x(2x) where x is the width, so P(x) = .25(x(2x)) is the amount of money he will pay for it. Set it equal to 200 because you know that's what he actually paid and solve for x.
Thanks for the explanation. However, I'm not quite sure why you simply multiply the cost by the area. Could you explain it in words? -
Date: Wed, Jan 26 2011 02:28:03
nateiskewl wrote: Thanks for the explanation. However, I'm not quite sure why you simply multiply the cost by the area. Could you explain it in words?
Because you said that "the lawn-care company charged $.25 per square foot." The total square footage is the area. -
Date: Wed, Jan 26 2011 02:33:31
AwonW wrote: Because you said that "the lawn-care company charged $.25 per square foot." The total square footage is the area.
Why does multiplying the total square footage by the price per single square foot give the total cost? Maybe a generalized explanation not involving this problem would help me understand. -
Date: Wed, Jan 26 2011 02:41:01
nateiskewl wrote: Why does multiplying the total square footage by the price per single square foot give the total cost? Maybe a generalized explanation not involving this problem would help me understand.
Uhh I don't really know how to explain this with a generalized explanation, but you can think about a problem in which someone is buying square ft tiles. If someone needed to fill a 4x4 ft floor with tiles how many tiles would they need? They'd need 16 right? And now if I told you each tile costs $2 how would you find out how much the total cost of the project is? -
Date: Wed, Jan 26 2011 02:53:44
AwonW wrote: Uhh I don't really know how to explain this with a generalized explanation, but you can think about a problem in which someone is buying square ft tiles. If someone needed to fill a 4x4 ft floor with tiles how many tiles would they need? They'd need 16 right? And now if I told you each tile costs $2 how would you find out how much the total cost of the project is?
Great, that helps a lot. It turns out this problem wasn't even on the homework I'm doing, but thanks anyway! -
Date: Wed, Jan 26 2011 04:04:05
number 35. D: I don't understand. -
Date: Wed, Jan 26 2011 04:09:29
Tetsip wrote: *pic* number 35. D: I don't understand.
They've given you the formula for radius based on volume. They also gave you the initial volume and the inflated volume. Parts 1 and 2 are easy. For the third part try manipulating the formula so you get it in terms of volume since you want to use radii to find an increase in volume. -
Date: Wed, Jan 26 2011 23:41:46
shit sorry guys, didn't even see that people were posting here (that's why i put bullet #2 up there lol, i don't check this unless people @mention me) looks like all the problems have been talked about though so far, thanks for the help guys @nateiskewl there are a few ways to help think about that concept: 1: if you dont care about why you can just do unit canceling. ([dollars]/[square feet])*([square feet]) the square feet cancel and you're left only with dollars 2: you can think about it as a ratio: .25 dollars / 1 square feet = x dollars / 200 square feet then just solve this for x (IE, the price per square foot is a ratio so you set up the same ratio on the other side but replace x for the value you don't know) 3: think of them as buying individual things. it's .25 dollars for 1 square foot (like the price of one pen or whatever) and you need 200 square feet (think of it like buying 200 pens for .25 dollars each) so you mulitply 200*.25 to get your total cost hope this helped some, it's hard to explain in typed media
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Date: Thu, Feb 3 2011 19:09:22
Graphs A and B are approximate graphs of f and f ' for f(x)=–x^2–8x–8. So f is decreasing (and f ' is negative) on the interval (a, infinity) for a=? help?
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Date: Thu, Feb 3 2011 19:24:35
I think you might need f'' for that.
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Date: Thu, Feb 3 2011 19:50:14
SJ wrote: Graphs A and B are approximate graphs of f and f ' for f(x)=–x^2–8x–8. So f is decreasing (and f ' is negative) on the interval (a, infinity) for a=? help?
take the derivative, let that equal zero, solve for x, that will be the vertex, which will be a -
Date: Thu, Feb 3 2011 21:43:06
you're looking for the point where f' is always negative right? so you solve for f' (2x-8) then solve for where that's always negative (2x=8 -> x=4) you can think about it in terms of the actual graphs, where does y=2x-8 cross the axis and become negative
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Date: Fri, Feb 4 2011 02:13:23
I'm taking Physics right now, so a lot of this stuff will be super easy for you. Last time I took physics was four years ago though, so I don't remember a thing. What net force is required to to accelerate a 60kg ice skater at 3m/s/s? Fnet=am ==> Fnet=3m/s/s*60==> Fnet=180N Correct? A child on roller skates undergoes an acceleration of .4m/s/s due to a horizontal net force of 24N. What is the mass of the child? Fnet=am so m=Fnet/a==> m=24N/.4m/s/s==> m=60kg Yes? These next two I can't figure out. "If a pull of 210 N accelerates a 40kg child on ice skates at a rate of 5m/s/s, what is the frictional force acting on the skates?" "A mother of mass 50kg and her daughter of mass 25kg are ice skating. They face each other, and the mother pushes on the daughter such that the daughter's acceleration is 2m/s/s. What is the force exerted by the mother on the daughter? What is the force exerted by the daughter on the mother? What is the mother's acceleration?"
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Date: Fri, Feb 4 2011 02:29:53
For the pull one calculate how much that force should accelerate the child, and then calculate how much net force is acting on the child to make him accelerate 5m/s^2. The difference between the two values will be the force of friction. For the daughter one calculate the force needed to accelerate the daughter 2m/s/s, then remember for every action there is an equal and opposite reaction, this is the force on the mother. horray for hijacking strats thread ;D
Mike wrote: I'm taking Physics right now, so a lot of this stuff will be super easy for you. Last time I took physics was four years ago though, so I don't remember a thing. What net force is required to to accelerate a 60kg ice skater at 3m/s/s? Fnet=am ==> Fnet=3m/s/s*60==> Fnet=180N Correct? A child on roller skates undergoes an acceleration of .4m/s/s due to a horizontal net force of 24N. What is the mass of the child? Fnet=am so m=Fnet/a==> m=24N/.4m/s/s==> m=60kg Yes? These next two I can't figure out. "If a pull of 210 N accelerates a 40kg child on ice skates at a rate of 5m/s/s, what is the frictional force acting on the skates?" "A mother of mass 50kg and her daughter of mass 25kg are ice skating. They face each other, and the mother pushes on the daughter such that the daughter's acceleration is 2m/s/s. What is the force exerted by the mother on the daughter? What is the force exerted by the daughter on the mother? What is the mother's acceleration?"
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Date: Fri, Feb 4 2011 02:30:24
Loanshark wrote: Bu-bu-but, light has momentum
Yeee :D Anyways Strat, Just wondering, very general question, you know how we take theorems and such for granted and how we can use them to solve problems "such as Pythagorean theorem or whatever", what if I needed to prove something which eventually lead to a very complex topic such as the Taylor Series Expansion of Exponential Functions where my findings for whatever task had to prove that the sum of the infinite series is essentially a^x or e^x ln a, which is already proven by the taylor series. Now would I have to PROVE and DERIVE the taylor series for my answer, which corresponds to my graphical analysis that i had to conduct, or can i simply take for granted that e^x ln a (which is proven by taylor series) was already proven to be a^x which coincidentally is the sum to infinity. Do i take this for granted or what? Because it is a pain to first derive this concept and then prove that the sum to infinity is already something we know (well sort of) Your thoughts? @strat1227 -Light -
Date: Fri, Feb 4 2011 02:37:31
The taylor series seems to be a well known proof, so no you don't have to prove it if you mention it when you use it. Why re-invent the wheel? I do think you are expected to be able to prove it if your using it though.
Light wrote: Yeee :D Anyways Strat, Just wondering, very general question, you know how we take theorems and such for granted and how we can use them to solve problems "such as Pythagorean theorem or whatever", what if I needed to prove something which eventually lead to a very complex topic such as the Taylor Series Expansion of Exponential Functions where my findings for whatever task had to prove that the sum of the infinite series is essentially a^x or e^x ln a, which is already proven by the taylor series. Now would I have to PROVE and DERIVE the taylor series for my answer, which corresponds to my graphical analysis that i had to conduct, or can i simply take for granted that e^x ln a (which is proven by taylor series), is something someone would generally know, and I wouldnt have to prove it. Your thoughts? -Light
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Date: Fri, Feb 4 2011 03:24:24
@Light depends on your professor, my classes are like 50/50 some classes want you to start from the beginning and others just want you to show it as simply as possible i'd ask your teacher
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Date: Fri, Feb 4 2011 05:07:35
@strat1227 A pipe with a radius of 2.5cm has water flowing it it at a velocity of .6m/s. The pipe rises up 18m where the radius has become 1.3cm. Find the velocity the water exits the pipe at. I thought this was a really easy problem at first, but I used 2 different methods and got 2 different answers. With Bernoulli's equation, I got 18.77m/s, but then I did it using A1V1 = A2V2, and got 2.21m/s, which sounded more reasonable. Did I do something wrong with Bernoulli's equation, or did I screw up something completely. This is my equation, after cancelling out terms. .5(.6)^2 = .5x^2 + (9.8)(18)
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Date: Fri, Feb 4 2011 07:13:39
@Loanshark looks like you're forgetting pressure? I'm no fluid dynamics pro but if i remember correctly bernoulli's equation has a term for pressure in it, and the pressure would increase as the pipe gets smaller no?
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Date: Fri, Feb 4 2011 08:07:48
oh hot dayum, i actually got the answer already LOL noice!!!
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Date: Fri, Feb 4 2011 08:32:21
If you have your slope and you have a point then you can calculate for b by substituting in your points into the parent graph equation. Just plug in (pi-3, 3) and you should get b out.
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Date: Fri, Feb 4 2011 08:41:47
-edit, sorry nevermind-
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Date: Fri, Feb 4 2011 10:36:48
[QUOTE=strat1227;60261]@strat1227
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Date: Fri, Feb 4 2011 16:12:05
@Loanshark yeah you've got to be doing something wrong because .6^2 / 2 = .18 and 9.8*18 is like 175, and since v^2 can't be negative there is not a solution to the equation you posted
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Date: Fri, Feb 4 2011 20:41:12
the water is moving at a constant rate through the pipe, the smaller end has to move the water through with more force, the pressure is greater at the smaller end. and if the pressure is the same on both ends, why would water flow at all?
Loanshark wrote: No, the pressure would decrease as the pipes get smaller O_o but Bernoulli's equation doesnt calculate internal pressure; it calculates external pressure, which would be the same at both ends, 1 atm @strat1227
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Date: Sat, Feb 5 2011 00:22:22
Awesome wrote: the water is moving at a constant rate through the pipe, the smaller end has to move the water through with more force, the pressure is greater at the smaller end. and if the pressure is the same on both ends, why would water flow at all?
According to Archimides principle, the faster water (or any fluid) moves, the less pressure there is it. The pressure would only really increase if you closed off the end if the pipe. And when I say the pressure is the same on both ends, I meant the pressure around the pipes :P not the pressure inside the pipes. -
Date: Sat, Feb 5 2011 01:27:24
Loanshark wrote: According to Archimides principle, the faster water (or any fluid) moves, the less pressure there is it. The pressure would only really increase if you closed off the end if the pipe. And when I say the pressure is the same on both ends, I meant the pressure around the pipes :P not the pressure inside the pipes.
After some googling it appears you're right. But it seems counter intuitive D: -
Date: Sat, Feb 5 2011 01:53:11
Yea I know right? I was kinda confused when I first heard it too. A good way to visualize it is to hold 2 pieces of paper parallel about a few cm apart and blow air between them. Moving fluid > lower pressure > paper moves towards each other
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Date: Sat, Feb 5 2011 07:11:55
Question; What type of atoms, and how many, are in a single molecule of: CH(subscript 3)COOH
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Date: Sat, Feb 5 2011 19:13:51
Its acetic acid, metabolite of ethanol (drinking alcohol) ;D carbon, hydrogen and oxygen 2 C 4 H 2 O each letter corresponds to an element on the periodic table, then its just a matter of counting, subscripts mean whatever before it, there is that many atoms of. so where there is a sub script 3 that means there is 3 Hydrogen
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Date: Sat, Feb 5 2011 19:32:19
Aww I wanted to get the question about vinegar
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Date: Sat, Feb 5 2011 19:45:41
@strat1227 Inside a NASA test vehicle, a 3.5 kg ball is pulled along by a horizontal ideal spring fixed to a friction- free table. The force constant of the spring is 225 N/m. The vehicle has a steady acceleration of 5.00 m/s2, and the ball is not oscillating. Suddenly, when the vehicle’s speed has reached 45.0 m/s, its engines turn off, thus eliminating its acceleration but not its velocity. Find (a) The amplitude of the resulting oscillation of the ball; (b) The frequency of the resulting oscillation of the ball; (c) What will be the ball’s maximum speed relative to the vehicle?
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Date: Sat, Feb 5 2011 22:02:06
a. F=ma to the left there's some spring force .5kx^2 and a is 5 and m is 3.5 so then you solve for the x that the spring is stretched and that'll be the amplitude once the a goes away b. w = sqrt(k/m) c. Vmax = Aw (amplitude * frequency)\ @Awesome
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Date: Sun, Feb 6 2011 20:37:21
@strat1227 does the time its accelerating play any role in the spring. would it get more compressed if it was accelerated longer? or do I just ignore the time part and for c) you mean Aw means amplitude * frequency right? not I take 2 variables and multiply them by that
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Date: Sun, Feb 6 2011 21:28:36
yeah i mean Aw = (amplitude * frequency) time doesn't matter, doesn't give you a time anyway so you don't know it
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Date: Sun, Feb 6 2011 21:32:31
if it accelerates at 5m/s^2 until it reaches 45m/s then it accelerates for 9 seconds. but since that doesn't matter its easy ;D thanks strat
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Date: Sun, Feb 6 2011 22:03:08
that's only if it started from rest, which the problem doesn't tell you, doesn't give you enough info to find time
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Date: Thu, Feb 10 2011 13:28:53
Ok I know this one should be pretty easy, but I lack theory on it, so help would be appreciated :/. The sooner the better. Bombing Lithium-6 isotope with deuterium particles ΔE=22.3MeV of energy was gained and two α particles Helium-4 were made, with the mass of 6.6467*10^-27 kg each. Find the mass of Lithium-6 isotope,. Sorry for raw translation, but I think you should get the idea.
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Date: Thu, Feb 10 2011 16:47:12
hmm i don't quite understand the setup lithium-6 is stationary and deuterium (no idea what that is) is being collided into it? i don't understand the translation lol
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Date: Thu, Feb 10 2011 16:49:06
yeah, you got it right. Deuterium is isotope of hydrogen, containing one proton and one neutron.
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Date: Thu, Feb 10 2011 16:52:57
is there a velocity of deuterium given? it looks like maybe a relativity problem just to make sure I have this right: to start we have lithium 6 + deuterium being collided into it. at the end we have 22.3MeV Energy, 2 alpha particles, and 2 Helium-4 Particles?
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Date: Thu, Feb 10 2011 17:01:50
well Helium-4 ARE alpha particles. We have lithium-6 + deuterium being collided into it, at the end we have 22.3MeV Energy and 2 alpha particles with the mass of 6.6467*10^-27 kg each. no velocity is given. Lol, I think right now I am starting to understand how to do this myself :D. EDIT: yeah, thanks, got the idea now xD.
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Date: Thu, Feb 10 2011 17:31:27
haha yeah then that's a binding energy (upper level chemistry) question, i know the concepts but not how to work the problems, sorry I couldn't help more but glad you got it xD
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Date: Fri, Feb 11 2011 17:40:06
Sketch the region enclosed by the given curves. Decide whether to integrate with respect to x or y. Then find the area of the region. y=e^(5x), y=e^(8x), x=1 so i find the intersection by setting e^(5x) and e^(8x) equal to each other which gives me x=0 so the intervals are 0 to 1. then i switch the equation in terms of y since its revolving around x=1 so they become (lny/5) and (lny/8) so the equation would be something like (integral sign) (intervals 0 and 1) pi*(lny/5)^2-(lny/8)^2) correct? i did that and got it wrong... also Find the volume of the solid formed by rotating the region enclosed by y=e^(5x+4) y=0 x=0 x=1 so in terms of y would be lny/(5x+4) then intervals 0 to 1? so itd be integrate intervals 0 to 1 of pi*(lny/(5x+4))^2?
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Date: Fri, Feb 11 2011 17:55:00
@SJ for the first one you're doing an integral in terms of dy, so you have to find the limits of y not x (you found the limits of x=0 to x=1, but you're not integrating in terms of x so that doesn't matter) For the second one you did the natural log wrong: y=e^(5x+4) ----> ln y = 5x+4 ----> x = (ln(y) - 4) / 5 I think that should solve your problems
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Date: Thu, Feb 17 2011 03:59:40
@Mike sup?
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Date: Thu, Feb 17 2011 04:01:23
What is the Earth's Centripetal acceleration given it's mass is 6x10^24 kg and it's radius from the sun is 1.5x10^11? I have no idea where to start.
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Date: Thu, Feb 17 2011 04:04:20
Force from gravity is (mMG)/(r^2) then you have F=ma so a=(MG)/(r^2) where M is mass of the sun G is gravitational constant and r is distance from sun @Mike
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Date: Thu, Feb 17 2011 04:17:51
@Mike are you sure they gave you only mass of the earth? mass of the earth cancels out, you need mass of sun only .. i just googled it to make sure i was remembering right and it agreed with me, so i'm not sure why they gave you not enough info
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Date: Thu, Feb 17 2011 05:34:22
@strat1227 Yeah, that's all they gave me. No Sun mass.
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Date: Thu, Feb 17 2011 14:30:12
@Mike that's not enough info then, no matter what method they want you to solve it with you need mass of the sun, acceleration will obviously vary depending on the source mass if i were you i'd just do it the way i showed and look up the sun's mass :dunno:
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Date: Thu, Feb 17 2011 15:26:46
Well, the other way without looking up for the mass of the sun would be to look up earth's period (e.g. one year, lol). a=v^2/r ; when v=s/t=(2(pi)*r)/T. therefore a=4(pi)^2*r/T Should work as well?
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Date: Thu, Feb 17 2011 16:25:49
@strat1227 No wonder I was so damn confused, I was missing information.
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Date: Thu, Feb 17 2011 17:19:32
Mike wrote: @strat1227 No wonder I was so damn confused, I was missing information.
As Raem showed you have enough information... -
Date: Thu, Feb 17 2011 17:59:29
@Awesome raem's answer isn't really right because it only works for a cirrcular path which the earth doens't follow, not even close really, it's very eliptical, but if you just call it a circle then yeah that works
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Date: Thu, Feb 17 2011 18:05:02
eccentricity of earth's orbit is something like 0.02 ; how is that 'not even close' to a circle?
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Date: Thu, Feb 17 2011 18:20:59
lol because that's over the course of the distance of earths orbit, which is of course gargantuan i've seen numbers closer to 5% generally but that doesn't change much dunno, i'm sure you're right and that's what mike's teacher wanted, just didn't pop into my mind because i wouldn't have thought of it as a circle :dunno:
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Date: Thu, Feb 17 2011 20:56:37
Why isn't it a circle? Like what explains earth's elliptical path that causes it to deviate so much from a circle anyway the values he was given have 1 and 2 sig figs its not like there is a great amount of accuracy being used here. good job Raem for figuring out how to do it with the information given ;D
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Date: Thu, Feb 17 2011 21:03:47
awesome: http://en.wikipedia.org/wiki/Orbital_eccentricity if epsilon = 0 then it's a circle otherwise it's what's displayed there
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Date: Thu, Feb 17 2011 21:55:16
ah cool stuff, so its caused from all the other planets and what not having gravity pulling earth?
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Date: Fri, Feb 25 2011 23:45:59
i have some questions to do for religion. 1)What happens to our life together when we sin?2)How can we live out our vacation in the image of god and create order in the world?3)What is the role of forgivness and reconciliation?
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Date: Sat, Feb 26 2011 00:08:04
penspinnerlin06 wrote: i have some questions to do for religion. 1)What happens to our life together when we sin?2)How can we live out our vacation in the image of god and create order in the world?3)What is the role of forgivness and reconciliation?
1. YOU GO TO HELL! 2. YOU CAN'T; YOU WILL GO TO HELL! 3. TO TRY NOT TO GO TO HELL, YOU HEATHEN. -
Date: Sat, Feb 26 2011 01:01:23
I divided by 0 successfully. What do I do now?
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Date: Tue, Mar 1 2011 23:32:46
@strat1227 I have a question in science: predict which current will be greater, the current passing through an electric iron or the current passing through an electric razor, when each is plugged into a 120 V outlet. I don't understand how to find the answer to that. Help D:
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Date: Tue, Mar 1 2011 23:34:49
@TheAafg lol yeah that's a weird fucking question ... it obviously depends on the resistance of whatever the object is i'd say it's a trick question and they're the same, i think there's a standard ohms for an electronic that plugs into a wall outlet but i honestly have no idea lol
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Date: Tue, Mar 1 2011 23:38:02
I would think the iron, cuz it needs to make so transform more energy for the heat, then the tiny movement the razor has, so the engineers will dump the internal resistance
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Date: Thu, Mar 3 2011 17:41:13
@strat1227 I need help with math ASAP, would appreciate it.
So here I got this. How do i do summation of the part in the part above. I have 22 variations of x and the same amount of y. and the averages of x and y.
I hope my question is clear enough?.
Edit: understood from shoutbox -
Date: Thu, Mar 10 2011 08:11:17
A rancher wants to fence in an area of 2000000 square feet in a rectangular field and then divide it in half with a fence down the middle parallel to one side. What is the shortest length of fence that the rancher can use? lol halp
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Date: Thu, Mar 10 2011 17:07:19
draw a diagram those help A=x*y P=2x+3y are your equations, you need to do some re-arranging, some substitution and some deriving. you wanna solve for x or y in P'=0
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Date: Fri, Mar 11 2011 01:24:51
ok ive tried all of these didnt work lol http://answers.yahoo.com/question/index?qid=20081104175853AAt9umV http://answers.yahoo.com/question/index?qid=20100401182812AAUOeRi http://answers.yahoo.com/question/index?qid=20091107112907AAu6rzf http://answers.yahoo.com/question/index?qid=20081201154908AAltOlm http://wiki.answers.com/Q/A_rancher_wants_to_fence_in_an_area_of_500000_square_feet_in_a_rectangular_field_and_then_divide_it_in_half_with_a_fence_down_the_middle_parallel_to_one_side._What_is_the_shortest_length_of_fence
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Date: Fri, Mar 11 2011 02:42:47
P=2x+3y A=200 (just add some zeros when you do it ;D) A=x*y 200=x*y x=200/y sub that back into perimeter P=2(200/y)+3y P=400/y+3y now we have an equation for permiter in terms of one variable, we want a local minimum value, easiest way is take the derivative and set to 0 P'=400/y^2+3 let P'=0 0=-400/y^2+3 3=400/y^2 400/3=y^2 solve from there, once you get y sub back into the original equation Try looking over the first principles and other basic stuff make sure you really get what calculus is.
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Date: Fri, Mar 11 2011 17:40:29
@Awesome wow i actually got it this time. thanks a bunch man. im just so bad at calc lolol haha
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Date: Fri, Mar 11 2011 21:32:11
calc composes so much of math, not to mention how amazing of a human achievement it is and what it allows us to do. get enthusiastic about it, it makes learning easier. you should learn the basics of it at least ;D
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Date: Mon, Mar 21 2011 05:14:06
can someone explain 4px(in the context of parabolas) to me? iv looked it up online and dont understand what ppl are saying =/
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Date: Mon, Mar 21 2011 23:36:28
boshi wrote: can someone explain 4px(in the context of parabolas) to me? iv looked it up online and dont understand what ppl are saying =/
p is a value that represents three things: 1. The distance from the vertex to the focus. 2. The opposite of the distance from the vertex to the directrix. 3. The direction the parabola faces. For vertical parabolas, they open up if the value of p is positive, and down if p is negative. For horizontal parabolas, they open right if the value of p is positive, and left if the value of p is negative. -
Date: Tue, Dec 11 2012 14:26:25
yea i think thats the wrong approach, its like spinning for the masses or spinning in front of experts a prestigious competition should be aimed at an informed audience
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Date: Tue, Dec 11 2012 15:24:48
whats the most efficient way to sort a million 32-bit integers ?
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Date: Tue, Dec 11 2012 18:04:37
Loanshark wrote: whats the most efficient way to sort a million 32-bit integers ?
no clue about most efficient. i could deduce a way to do it, but can't guarantee it'd be the most efficient. you need a textbook or something to tell you that -
Date: Tue, Dec 11 2012 18:13:51
Loanshark wrote: whats the most efficient way to sort a million 32-bit integers ?
Sort in what way? Do you mean, highest to lowest? -
Date: Tue, Dec 11 2012 18:23:33
How would you work out the probability of wining the lottery? @strat1227
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Date: Tue, Dec 11 2012 18:43:11
Supergirl wrote: How would you work out the probability of wining the lottery? @strat1227
depends on what lottery it is. some of them they pick one winner out of all the tickets bought, others (like powerball) aren't dependent on how many people bought it at all -
Date: Tue, Dec 11 2012 21:12:17
Supergirl wrote: How would you work out the probability of wining the lottery? @strat1227
Easy. 0% -
Date: Wed, Dec 12 2012 01:58:42
Just use bubble sort! Sure its hugely inefficient for this number but it will work and you can get on with your life. Otherwise go check out wikipedia's article on sorting algorithms and figure out how to implement one of the more efficient ones.
Loanshark wrote: whats the most efficient way to sort a million 32-bit integers ?
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Date: Wed, Dec 12 2012 06:42:34
Loanshark wrote: whats the most efficient way to sort a million 32-bit integers ?
Merge sort that shit son, O(nlogn) -
Date: Wed, Dec 12 2012 06:45:34
Awesome wrote: Just use bubble sort! Sure its hugely inefficient for this number but it will work and you can get on with your life. Otherwise go check out wikipedia's article on sorting algorithms and figure out how to implement one of the more efficient ones.
Bubble sort is O(n^2) isn't it? Might as well be doing insertion sort at this point -
Date: Wed, Dec 12 2012 08:49:46
Do people still do bubblesorting? Why not use quicksort? Or you could use bogosort. :trollface:
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Date: Fri, Dec 14 2012 00:28:58
Supergirl wrote: How would you work out the probability of wining the lottery>
Like Strat said, it depends on the lottery. Normally in bigger lotteries a machine is used to select numbered balls. http://www.youtube.com/watch?v=Vc_PRhQpeJI Using Powerball as an example: There are 59 white balls, from which 5 are drawn. There are also 35 "Powerballs", from which 1 is drawn. To win the jackpot you must match all 6 numbers. [Wikipedia] [A] There are 59C5 ("59 choose 5") possible ways of selecting 5 white balls from the 59. Only one set of the 5 numbers is correct, so the probability of matching all 5 numbers is 1/(59C5) = 1/5006386 [B] There are 35 possible ways of selecting 1 Powerball from the 35. Only one number is correct, so the probability of choosing the correct number is 1/35 A rule of probability states that if two events are independent, the probability of both events occurring is equal to the probability that the first event occurs, times the probability that the second event occurs. In other words, the probability that the 5 white balls and 1 Powerball are matched correctly is equal to (1/5006386)*(1/35) = 1/175223510 So the probability of winning the Powerball jackpot is 1 in 175,223,510 To put the number into perspective, the probability of flipping a fair coin 27 times and getting 27 Heads in a row is 1 in 134,217,728.