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Is enough information given to solve this problem?

2Xtreme21

2Xtreme21

Diamond Member
So I'm taking the easiest physics class on the planet and one of the questions on my homework (created by the prof who isn't the sharpest tool in the shed) asks this:

A ball released from rest and rolling down an inclined plane covers 4 m in 9 s. What distance from the release point will the ball be located in 27 s?

I've taken 3 years of Physics already and I honestly don't think there's enough information given in the problem to solve this-- namely the angle of the plane. Is it solvable without knowing this?

And the answer isn't 12 (at least according to the web-based-submit-your-answer-and-I'll-tell-you-if-you're-right-or-wrong interface).
 
It is possible. You can find the angle of the plane from the first bit of information.

Sure, you could make it impossible to solve by making odd assumptions. But with the most realistic assumptions, it is solvable.
 
Originally posted by: dullard
It is possible. You can find the angle of the plane from the first bit of information.

Sure, you could make it impossible to solve by making odd assumptions. But with the most realistic assumptions, it is solvable.
Click to expand...

what he said 😛
 
I have to disagree with the naysayers about 12 being wrong. Simple algebra would indicate that it *is* 12 - then again, that's algebra, and I never took physics.
 
Originally posted by: aloser
I have to disagree with the naysayers about 12 being wrong. Simple algebra would indicate that it *is* 12 - then again, that's algebra, and I never took physics.
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Have to account for the ball accelerating down the slope. 😉
 
Originally posted by: aloser
I have to disagree with the naysayers about 12 being wrong. Simple algebra would indicate that it *is* 12 - then again, that's algebra, and I never took physics.
Click to expand...

12 does seem like it would be the answer, but if the ball is still acellorating (I never tood spelling class 😛), then it would be farther than 12m. I just don't know how to figue that out without the angle of the plan. So my vote goes for not enough information.
 
Originally posted by: jimbob200521
Originally posted by: aloser
I have to disagree with the naysayers about 12 being wrong. Simple algebra would indicate that it *is* 12 - then again, that's algebra, and I never took physics.
Click to expand...

12 does seem like it would be the answer, but if the ball is still acellorating (I never tood spelling class 😛), then it would be farther than 12m. I just don't know how to figue that out without the angle of the plan. So my vote goes for not enough information.
Click to expand...

you can figure the acceleration of the ball...
 
Why would you waste time figuring out the angle? Just avoid that and setup your axis so that the ball travels parallel to x, therefore the angle is 0 in your local coordinate system. Now its just a matter of finding out the acceleration and then carrying that through for 27s
 
Originally posted by: aloser
I have to disagree with the naysayers about 12 being wrong. Simple algebra would indicate that it *is* 12 - then again, that's algebra, and I never took physics.
Click to expand...
12 is correct, if you have some unusual new length unit. I assign you, aloser, the task of telling us how long your new unit is. That is, what does 1 Aloser equal in feet or meters?
 
Originally posted by: RGUN
Why would you waste time figuring out the angle? Just avoid that and setup your axis so that the ball travels parallel to x, therefore the angle is 0 in your local coordinate system. Now its just a matter of finding out the acceleration and then carrying that through for 27s
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ding ding ding.

Plenty of information. Don't over complicate.
 
12 is definitely not right. As long as it's not some sort of trick question then you've got enough info to figure out acceleration (which is constant).

Everything is there, and the answer is a nice number.
 
Assuming constant velocity it's solvable from the nine second mark to the 27 second mark it's solvable.

If there's acceleration involved, it's unsolvable. You don't have the angle of the plane. If the plane is 30 degrees to the ground it will accelerate slower than a plane 80 degrees to the ground.

All those people above me, how can you find acceleration with no known change in velocity and no known angle of the plane? Assume it's 90 degrees and use 9.8 m/s^2?
 
Originally posted by: fishmonger12
Assuming constant velocity it's solvable.

If there's acceleration involved, it's unsolvable. You don't have the angle of the plane. If the plane is 30 degrees to the ground it will accelerate slower than a plane 80 degrees to the ground.

How can you find acceleration with no known change in velocity???
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Wrong. It's rolling down an inclined PLANE. You know how fast the ball has already accelerated. As long as there is nothing screwy with gravity the acceration is going to be constant.
 
Originally posted by: fishmonger12
Assuming constant velocity it's solvable from the nine second mark to the 27 second mark it's solvable.

If there's acceleration involved, it's unsolvable. You don't have the angle of the plane. If the plane is 30 degrees to the ground it will accelerate slower than a plane 80 degrees to the ground.

All those people above me, how can you find acceleration with no known change in velocity and no known angle of the plane? Assume it's 90 degrees and use 9.8 m/s^2?
Click to expand...


Ball starts at rest and covers 4m in 9 seconds. Avg velocity is 4/9 m/s. Assuming constant acceleration (normal perfect world physics problem) the acceleration is 8/9 m/(s^2).
 
Originally posted by: Savij
Originally posted by: fishmonger12
Assuming constant velocity it's solvable.

If there's acceleration involved, it's unsolvable. You don't have the angle of the plane. If the plane is 30 degrees to the ground it will accelerate slower than a plane 80 degrees to the ground.

How can you find acceleration with no known change in velocity???
Click to expand...


Wrong. It's rolling down an inclined PLANE. You know how fast the ball has already accelerated. As long as there is nothing screwy with gravity the acceration is going to be constant.
Click to expand...

my feeble mind wonders about friction
 
Originally posted by: scorpmatt
my feeble mind wonders about friction
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Originally posted by: 2Xtreme21
So I'm taking the easiest physics class on the planet and ...
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I bet if 2Xtreme21 showed us his homework, it would say to ignore friction. 😉
 
Originally posted by: scorpmatt
Originally posted by: Savij
Originally posted by: fishmonger12
Assuming constant velocity it's solvable.

If there's acceleration involved, it's unsolvable. You don't have the angle of the plane. If the plane is 30 degrees to the ground it will accelerate slower than a plane 80 degrees to the ground.

How can you find acceleration with no known change in velocity???
Click to expand...


Wrong. It's rolling down an inclined PLANE. You know how fast the ball has already accelerated. As long as there is nothing screwy with gravity the acceration is going to be constant.
Click to expand...

my feeble mind wonders about friction
Click to expand...

You forgot about wind resistance too. And what about manetic fields. You can complicate this as much as you want and come up with 1 billion reasons why you can't solve it (maybe the entire plane is being rotated about some point). I'm assuming this is a simple acceleration and distance problem.
 
yeah, i took that same class in high school. every problem involved conditions like "assume there's no friction" or "assume earth isnt moving."
 
Originally posted by: dullard
It is possible. You can find the angle of the plane from the first bit of information.

Sure, you could make it impossible to solve by making odd assumptions. But with the most realistic assumptions, it is solvable.
Click to expand...

I agree that it's possible, but why would you need/want to know the angle of the plane? Isn't the acceleration all you need to solve the problem?
 
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