The homework help thread...(SERIOUS)

[ocarinanoob]

I've got a question about relativity. It's not in the coursework until next year. I was able to understand the basic concepts of it though.

How exactly does time go backwards if you're travelling faster than light? (not technically possible, just a thought)

I understand if you got faster time slows for you in the observer's frame of reference, but once you reach a speed faster than c, how does time go backwards? Is such a thing even possible?

Secondly, if light behaves like a wave, what medium does it travel in? It actually travels fastest in a vacuum... why? It shouldn't be able to travel at all.

[Cell-Tech]

I've got a question about relativity. It's not in the coursework until next year. I was able to understand the basic concepts of it though.

How exactly does time go backwards if you're travelling faster than light? (not technically possible, just a thought)

I understand if you got faster time slows for you in the observer's frame of reference, but once you reach a speed faster than c, how does time go backwards? Is such a thing even possible?

Try reading this: http://en.wikipedia.org/wiki/Time_tr...8FTL.29_travel

Secondly, if light behaves like a wave, what medium does it travel in? It actually travels fastest in a vacuum... why? It shouldn't be able to travel at all.

That's a really good question. Electromagnetic waves (which is what light is) are unique in that they can propagate through empty space. Electric and magnetic fields can exist in a vacuum. Electromagnetic waves occur when electromagnetic fields are waving.

[jimmybimmy]

Try reading this: http://en.wikipedia.org/wiki/Time_tr...8FTL.29_travel



That's a really good question. Electromagnetic waves (which is what light is) are unique in that they can propagate through empty space. Electric and magnetic fields can exist in a vacuum. Electromagnetic waves occur when electromagnetic fields are waving.

This ^

[Futurebound]

I've got a question about relativity. It's not in the coursework until next year. I was able to understand the basic concepts of it though.

How exactly does time go backwards if you're travelling faster than light? (not technically possible, just a thought)

I understand if you got faster time slows for you in the observer's frame of reference, but once you reach a speed faster than c, how does time go backwards? Is such a thing even possible?

Secondly, if light behaves like a wave, what medium does it travel in? It actually travels fastest in a vacuum... why? It shouldn't be able to travel at all.

Well I figured when you travel FTL you go passed the light in the passed
meaning you could catch up to light on earth thousands of years ago billions of light years away and see it (assuming you have the technolagy capable of viewing something so small)
science junky here, dont take this as fact
just how i rationalized it

[NeverPity]

Seriously need help on this, I was absent a few days and cannot solve these..idk how to work with the degrees it is new to me. I need all of the variables/equations and an answer please. Just 4 questions. Reps on sight if someone does these, reply here or PM me please.

1)in a scene in an action movie,a stuntman jumps from the top of one building to the top of another building 4.0 m away.after a running start,he leaps at an angle pf 15 degree with repect to the flat roof while traveling at a speed of 5.0m/s.will he make it to the other roof ,which is2.5m shorter the the building he jumps from?

2)A golfer hits a gold ball at an angle of 25 degrees to the ground. if the golf ball covers a horizontal distance of 301.5 m, what is the balls max height?

3) a baseball is thrown at an angle of 25 degrees relative to the ground at a speed of 23 m/s. if the ball was caught 42 m from the thrower, how long was it in the air. how high did the ball travel before being caught?

4)salmon often jump waterfalls to reach their breeding grounds.starting 2.00m from a waterfall 0.55m in height at what minimum speed must a samon jumping at an angle of 32.0 degree leave the water to continue upstream

THANKS

[jimmybimmy]

Seriously need help on this, I was absent a few days and cannot solve these..idk how to work with the degrees it is new to me. I need all of the variables/equations and an answer please. Just 4 questions. Reps on sight if someone does these, reply here or PM me please.

1)in a scene in an action movie,a stuntman jumps from the top of one building to the top of another building 4.0 m away.after a running start,he leaps at an angle pf 15 degree with repect to the flat roof while traveling at a speed of 5.0m/s.will he make it to the other roof ,which is2.5m shorter the the building he jumps from?

2)A golfer hits a gold ball at an angle of 25 degrees to the ground. if the golf ball covers a horizontal distance of 301.5 m, what is the balls max height?

3) a baseball is thrown at an angle of 25 degrees relative to the ground at a speed of 23 m/s. if the ball was caught 42 m from the thrower, how long was it in the air. how high did the ball travel before being caught?

4)salmon often jump waterfalls to reach their breeding grounds.starting 2.00m from a waterfall 0.55m in height at what minimum speed must a samon jumping at an angle of 32.0 degree leave the water to continue upstream

THANKS

I'm not going to actually do your home work for you. But look at this video, helps a lot; if you can't do this part of physics you'll be screwed.

http://www.youtube.com/watch?v=-uUsUaPJUc0

http://www.youtube.com/results?searc...ojectile+motio

[LeonRokky]

all subjects welcome?

[TorakFirenze]

all subjects welcome?

Yupzors

[diamonds123]

good idea, i fu**** hate homework,

[ocarinanoob]

Well I figured when you travel FTL you go passed the light in the passed
meaning you could catch up to light on earth thousands of years ago billions of light years away and see it (assuming you have the technolagy capable of viewing something so small)
science junky here, dont take this as fact
just how i rationalized it

Interesting...

But as I understand it in that case if you go faster than light you're not doing anything special. You're just going faster than light at the present. Since there is no physical past or future you simply won't see that light. The light in the past doesn't exist anymore. Light that was there 1 second ago becomes light right now. I.e. the past becomes the present, and if you travel faster than light the light is still going at our time frame. You'll see darkness.

EDIT: Realized c is always constant... doesn't that mean if you're traveling faster than c, light will still travel faster than you? E.g. if your speed is c and you're racing a beam of light, the speed of that beam of light will become 2c. Right? Hence time slows even more. But how will you be traveling back in time? You're just in super slow motion...

Someone please correct my understanding.

I don't get how you can go back in time via the FTL method... :/

[ANDYMAYNE]

Please help me with Physics. I cannot afford to fail another test. I cannot find the formulas. If you provide me with a formula please tell me what the symbols stand for. Thank you for any help you can offer.

1. An archer shoots an arrows horizontally at a target 15m away. The arrow is aimed directly at the center of the target, but it hits 52cm lower. What was the initial speed of the arrow?

2. The great, gray-green, greasy Zambezi Ricer flows over Victoria Falls in south central Africa. The falls are approximately 108m high. If the river is flowing horizontally at 3.60m/s just before going over the falls, what is the speed of the water when it hits the bottom? Assume the water is in freefall as it drops.

3. A driver runs horizontally off the end of a diving board with an initial speed of 1.75m/s. If the diving board is 3.00m above the water, what is the diver's speed just before she enters the water?

[AmarjotPandher]

i need to write a children's story and i need a topic

[FatAli]

Please help me with Physics. I cannot afford to fail another test. I cannot find the formulas. If you provide me with a formula please tell me what the symbols stand for. Thank you for any help you can offer.

1. An archer shoots an arrows horizontally at a target 15m away. The arrow is aimed directly at the center of the target, but it hits 52cm lower. What was the initial speed of the arrow?

2. The great, gray-green, greasy Zambezi Ricer flows over Victoria Falls in south central Africa. The falls are approximately 108m high. If the river is flowing horizontally at 3.60m/s just before going over the falls, what is the speed of the water when it hits the bottom? Assume the water is in freefall as it drops.

3. A driver runs horizontally off the end of a diving board with an initial speed of 1.75m/s. If the diving board is 3.00m above the water, what is the diver's speed just before she enters the water?

1. http://answers.yahoo.com/question/in...4232001AAmTcgT

2. http://answers.yahoo.com/question/in...6155742AAuxyDu

3. http://answers.yahoo.com/question/in...6054725AAUeLoS


just answers.yahoo.com the question

[JoeSmoe32]

Interesting...

But as I understand it in that case if you go faster than light you're not doing anything special. You're just going faster than light at the present. Since there is no physical past or future you simply won't see that light. The light in the past doesn't exist anymore. Light that was there 1 second ago becomes light right now. I.e. the past becomes the present, and if you travel faster than light the light is still going at our time frame. You'll see darkness.

EDIT: Realized c is always constant... doesn't that mean if you're traveling faster than c, light will still travel faster than you? E.g. if your speed is c and you're racing a beam of light, the speed of that beam of light will become 2c. Right? Hence time slows even more. But how will you be traveling back in time? You're just in super slow motion...

Someone please correct my understanding.

I don't get how you can go back in time via the FTL method... :/

Your getting ahead of yourself. Einstein based his entire theory of relativity around the fact that the speed of light was a sort of universal speed limit. He assumed that nothing can go faster than the speed of light.

While you are right about the speed of light being constant in all frames of reference, you are wrong about you, yourself, traveling at the speed of light. Any object without mass cannot travel at the speed of light, according to the theory of relativity. You can theoretically get to 0.9999c but will never reach 1.0c as long as you contain any mass.

You also added their velocities which is a Newtonion physics principle and is not relativistic. Newtonion physics predicts that if you are traveling 0.5c then the light you see must be going 1.0c. To an outside observer this would mean that the light appears to be going 1.5c, which goes directly against Einstein's "universal speed limit" notion. In relativistic physics velocities are not added, but rather ran through the following equation

Applying this equation on our example we get (1.5c) / (1 + (.5c^2 / c^2)) which simplifies to (1.5c / 1.5) or just c. So to an outside observer the light that you see traveling at 0.5c is going the same speed as it would appear to be for someone who is standing still.

Under classic relativity faster than light isn't possible. It has been theorized though that there are particles that never go from being slower than the speed of light to faster, but have always been and always will be going faster than the speed of light. There is also some questionable laboratory findings from Europe that found faster than the speed of light travel. See the article here http://ibnlive.in.com/news/would-ein...187145-11.html

I'd suggest reading a translated version of Eintstein's original papers regarding relativity. They will walk you along the steps to understand why such things as time dilation and length contraction are really needed. It's definitely slow reading but even without proper knowledge of physics and math you can still grasp the general concepts quite well. Supplement that reading with youtube visuals and other readings and you should be set. Good luck!

EDIT: Wish I was being taught this stuff in high school...

[ocarinanoob]

^ Thank you for the explanation.

I'm not being taught this at highschool, but I'm interested so I just want to investigate on my own. I'll try read up on Einstein's papers. I have a few more questions though (if you don't mind answering):

1. I don't get what you said here:

" So to an outside observer the light that you see traveling at 0.5c is going the same speed as it would appear to be for someone who is standing still. "

The equation works but what is the reason for this? Is this because your time is going half as fast as the observer's time if you're moving at 0.5c? And light is somehow moving at 0.5c but it appears to be moving at 1c because of time dilation?

2. Okay, so its established that you can't reach c unless you have no mass. But, say, you were somehow able to (thought experiment). What would happen? And what would happen if you go faster than c (breaking rules again here)?

Thanks again.

[ocarinanoob]

I'm becoming a frequent poster in this thread... it's quite helpful.

Does anyone have a way to write a rule for a sequence in terms of n without a lot guesswork? E.g. are there any solid rules that I need to follow that will help me get the correct formula for a sequence?

It currently takes me a lot of trial and error to get the right eqn.

[jbball92]

^ Thank you for the explanation.

I'm not being taught this at highschool, but I'm interested so I just want to investigate on my own. I'll try read up on Einstein's papers. I have a few more questions though (if you don't mind answering):

1. I don't get what you said here:

" So to an outside observer the light that you see traveling at 0.5c is going the same speed as it would appear to be for someone who is standing still. "

The equation works but what is the reason for this? Is this because your time is going half as fast as the observer's time if you're moving at 0.5c? And light is somehow moving at 0.5c but it appears to be moving at 1c because of time dilation?

2. Okay, so its established that you can't reach c unless you have no mass. But, say, you were somehow able to (thought experiment). What would happen? And what would happen if you go faster than c (breaking rules again here)?

Thanks again.

1. think about when your driving. your going 50mph and another guy is going 80mph, to you it appears he is going 30mph because your already going 50mph, and relative to you, he is going 30mph faster. but to an observer the guy appears to be going 80mph because the observer isnt moving. (like when you are next to someone on the highway going the same speed, neither of you appear to be moving relative to eachother).

2. the simple answer, which is frustrating, its impossible, because it would require infinite energy. the answer you want, you become infintlely massive and infinietly energetic. cant answer the second part though, I suggest you read about Tachyons > http://en.wikipedia.org/wiki/Tachyon

[ocarinanoob]

jbball92-

For 1. But isn't light constant for everyone? If you assume light goes at 80mph (for simplicity's sake) then even if you're going 50mph and there is light travelling at 80mph in the same direction as you, it would still seem to be travelling at 80mph to you.

2. Infinitely massive and infinitely energetic? What would something with those properties behave like? I also read about Tachyons, I still didn't get my answer... Do tachyons distort time (if they exist)?

[jbball92]

jbball92-

For 1. But isn't light constant for everyone? If you assume light goes at 80mph (for simplicity's sake) then even if you're going 50mph and there is light travelling at 80mph in the same direction as you, it would still seem to be travelling at 80mph to you.

2. Infinitely massive and infinitely energetic? What would something with those properties behave like? I also read about Tachyons, I still didn't get my answer... Do tachyons distort time (if they exist)?

honestly I suck at explantions. but essentially the speed light would APPEAR to be would be light speed -your speed. i.e. 80-50=30mph, BUT it would always be that 80mph,even though it seems slower to you.
hope this helps a bit....the history channel did an amazing job. Its one of those things you gotta see

[smbrown3706]

can anyone help me out with any of these questions?

Too many questions so I'll just do the first and explain the rest.
3.a. Factor into (2x^2 - 2)(x - 3) or even further into (2x + 2)(x - 1)(x - 3) = 0, set each = to 0 and you get x = -1, 1, 3
For part b, I'm not sure what they want you to divide by? Maybe choose a factor and divide by it, i.e. divide the equation by (2x + 2), then that result by (x - 1)?
Parts c, d, e look straightforward.
4.a. To find the domains the trick is to find where the denominator is equal to zero and say that the domain is all numbers except for those which the denominator is equal to zero.
b. x intercepts you just see where the equation = 0, y intercept you just plug in x = 0 (if 0 is in the domain)
c. vertical asymptotes will be where the domain is invalid, idk where a horizontal one would be though since I haven't graphed the functions, sorry

[JoeSmoe32]

^ Thank you for the explanation.

I'm not being taught this at highschool, but I'm interested so I just want to investigate on my own. I'll try read up on Einstein's papers. I have a few more questions though (if you don't mind answering):

1. I don't get what you said here:

" So to an outside observer the light that you see traveling at 0.5c is going the same speed as it would appear to be for someone who is standing still. "

The equation works but what is the reason for this? Is this because your time is going half as fast as the observer's time if you're moving at 0.5c? And light is somehow moving at 0.5c but it appears to be moving at 1c because of time dilation?

To clarify, if you were traveling at 0.5c any light that you would see would appear to be going at 1.0c. Now, if you were to fly past someone who is stationary while you were going 0.5c, they would also see the same light going at 1.0c.

The reason that this happens is the single most difficult to grasp, and also the most important, notion in all of relativity. It is the combination of time dilation and length contraction that happens on a local level that causes the same beam of light to be going at the same speed to both observers.

Perhaps a slightly different way of thinking about it would make it clearer. The speed of light is constant all the time, no matter how much time dilation or length contraction you have it still goes 1.0c. A stationary observer, traveling at 0.0c, sees a beam of light traveling at 1.0c. Another observer, cruising by in his Corvette at 0.5c, sees the same beam of light traveling at 1.0c.

Now, the only different between these two observers is their speed. Their speed causes a deformation in the space-time continuum, causing a time dilation and length contraction. The man in the Corvette creates a much, much bigger deformation in this continuum because his speed is so great. This deformation acts as a sort of "fixer" term in a sense that it slows down time and shrinks length so that the speed of light travels at 1.0c in his frame of reference.

You have the basic idea down, hopefully my explanations helped to further your understanding and didn't confuse you further.

2. Okay, so its established that you can't reach c unless you have no mass. But, say, you were somehow able to (thought experiment). What would happen? And what would happen if you go faster than c (breaking rules again here)?

Thanks again.

The closer that you get to the speed of light the amount of energy required to accelerate increases exponentially. To reach the speed of light would require an infinite amount of energy, which is impossible.

But assuming that you could in some odd way get to it, the result would most likely be quite boring. Visually, as you near the speed of light your vision would become one bright singularity. This picture below gives you the idea. (More info here http://math.ucr.edu/home/baez/physic...spaceship.html)


Just a quick disclaimer everything from this point on is from my best knowledge and intuition on the subject and not backed up with any data whatsoever. So take it with a grain of salt. But as you pass the speed of light you would be going faster than the light you see and thus it will never reach you. Your eyes will not see any light whatsoever, you will be traveling in complete and utter blackness. As you travel you will be tugged this way and that in different directions by different galactical gravitation pulls. Now assuming you made it out of our known universe (which you eventually would, because nothing can propagate faster than the speed of light) without getting pulled into a black hole, you would continue to fly blindly through the universe. However without the tug of different gravities you would feel as if you were standing still. So you would live out the rest of your years in utter blackness in what you would think would be a stationary environment. You would live, just like any human being, until you were 80 or 90 or maybe even 100 if you took your multi and lifted heavy. Your local sense of time would not be deformed whatsoever.

However, if you could somehow peep at earth you would see that it has aged many times faster than you have until you reach the speed of light. After you pass the threshold of the speed of light I honestly cannot tell you what the Earth would do in relation to you. I know that is really what you were looking for but it is beyond my scope of understanding. I'm sure a few hours on google though and you could find an answer.

Whew...

[ocarinanoob]

Wow thanks ALOT! You made it alot easier to understand. Measly repped

[TrvsMeltn28]

I'm a full time college student and full time worker. I would like to know if anyone has any tips on how to schedule the best time to do homework around work, school, and lifting. I have had a rough time figuring out a good time I'n between these things.

[smbrown3706]

I'm a full time college student and full time worker. I would like to know if anyone has any tips on how to schedule the best time to do homework around work, school, and lifting. I have had a rough time figuring out a good time I'n between these things.

Easiest thing I found was to wake up super early and lift, then get school work and work work done during day, go to sleep as early as possible and repeat.

[StillScared]

Too many questions so I'll just do the first and explain the rest.
3.a. Factor into (2x^2 - 2)(x - 3) or even further into (2x + 2)(x - 1)(x - 3) = 0, set each = to 0 and you get x = -1, 1, 3
For part b, I'm not sure what they want you to divide by? Maybe choose a factor and divide by it, i.e. divide the equation by (2x + 2), then that result by (x - 1)?
Parts c, d, e look straightforward.
4.a. To find the domains the trick is to find where the denominator is equal to zero and say that the domain is all numbers except for those which the denominator is equal to zero.
b. x intercepts you just see where the equation = 0, y intercept you just plug in x = 0 (if 0 is in the domain)
c. vertical asymptotes will be where the domain is invalid, idk where a horizontal one would be though since I haven't graphed the functions, sorry

TO find horizonal asymptotes do this
say your given x^2 +1 / x^2 -x -2
divide both top and bottom by highest powers of x that is x^2
so you have 1+(1/x^2) / (1-1/x-2/x^2)
then find what happens when x-> infinity.
in this case when x approaches infinity y -> 1
therefore y=1 is a horizontal asymptote.

[jurkajurkajur]

1
___________ = ?

1 + v2 - v3

[Jake6977]

I get 1 % extra credit in AP stats if I can prove these two equations are equal, algebraically. They are the two formulas for variance in a discrete frequency distribution.
σ^2= ∑[(x-μ)^2*p(x)]
σ= ∑[x^2*p(x)]-μ^2

Any help would be greatly appreciated!

[benchpresschick]

Any tips for memorizing poems? Don't want to do this I'm really bad at memorizing things that don't have a use.. but have to and I have no idea how to go about it.. Saying it out loud doesn't seem to be helping..

[jbball92]

Any tips for memorizing poems? Don't want to do this I'm really bad at memorizing things that don't have a use.. but have to and I have no idea how to go about it.. Saying it out loud doesn't seem to be helping..

honestly, just keep practicing it. had to memorize monologs from Julius Caesar senior yr, just go one line at a time tbh.

[SportbikerKid]

I get 1 % extra credit in AP stats if I can prove these two equations are equal, algebraically. They are the two formulas for variance in a discrete frequency distribution.
σ^2= ∑[(x-μ)^2*p(x)]
σ= ∑[x^2*p(x)]-μ^2

Any help would be greatly appreciated!

What are the bounds of the sum and what variable is being summed?