# Physics multiple choice mass, acceleration, velocity based question

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Thread starter 5 months ago
#1
This is the question:

Two unpowered toy cars, P and Q, are released from rest from X and travel down the track to Y. Car P has twice the mass of car Q. There is negligible friction. What quantity is the same for car P and car Q?

a) the gravitational potential at X
b) the accelerating force at X
c) the velocity when they arrive at Y
d) the momentum when they arrive at Y

I initially thought that the answer was b (the accelerating force at X) but then found out that the answer was c (the velocity). Could someone please explain how the answer is c because I'm not sure how to explain it. Thanks.
0
5 months ago
#2
b says accelerating force, which means resultant force = mg sin theta
So it depends on mass
Speed does not depend on mass
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Thread starter 5 months ago
#3
(Original post by Aung)
b says accelerating force, which means resultant force = mg sin theta
So it depends on mass
Speed does not depend on mass
Thanks Aung.
0
5 months ago
#4
ceg250 . There is still an issue with this question.
Is the answer a) copied correctly?
Last edited by Stonebridge; 5 months ago
0
5 months ago
#5
(Original post by Stonebridge)
ceg250 . There is still an issue with this question.
Is the answer a) copied correctly?
Oh right.
If it says gravitational potential, a is also correct.
Because gravitational potential only depends on mass of Earth and distance from centre.
If it says gravitational potential energy, it also depends on mass of car.
G.P = -GM/r
G.P.E = -GMm/r

But even if the question is copied correctly, it is more likely to be c.
Because although GPE is taught since year9/year10, GP is only taught in year13.
So if this is an AS question, we don't need to consider about it.
Last edited by Aung; 5 months ago
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5 months ago
#6
If more than one answer is allowed, then a) is certainly also correct.
I suspect, though, that only one correct answer is allowed, which means we have to conclude that
either
it is a typo and should have been 'gravitational potential energy'
or
it's a really poor physics question that somehow got through the shredding process.
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Thread starter 5 months ago
#7
(Original post by Stonebridge)
If more than one answer is allowed, then a) is certainly also correct.
I suspect, though, that only one correct answer is allowed, which means we have to conclude that
either
it is a typo and should have been 'gravitational potential energy'
or
it's a really poor physics question that somehow got through the shredding process.
Hi Stonebridge,

Yeah just realised it was a typo it was supposed to be gravitational potential energy. Sorry about that. Thanks for all the help.
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