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A wagon is coasting at a speed $v_A$ along a straight and level road. When 42.5% of the wagon's mass is thrown off the wagon, parallel to the ground and in the forward direction, the wagon is brought to a halt. If the direction in which this mass is thrown is exactly reversed, but the speed of this mass relative to the wagon remains the same, the wagon accelerates to a new speed $v_B$. Calculate the ratio $\frac{v_B}{v_A}$.

A tricky one!

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what is supposed to be tricky about this? that the fraction is irrelevant? – user2963 Mar 14 '12 at 0:17
Take note of the part of the FAQ that says that we do not do homework here, but answer conceptual physics questions. Manishearth's answer is consistent with that policy. – dmckee♦ Mar 14 '12 at 1:40
@dmckee inconsistent or 'is consistent'? Yes, I know my answer has no concept it it.. I'll delete it if you want... – Manishearth♦ Mar 14 '12 at 1:44
@Manishearth The latter. Enter moderator superpowers for editing comments older than five minutes. – dmckee♦ Mar 14 '12 at 1:47
How is the fraction not relevant, dont lighter masses travel faster – Uconn Mar 14 '12 at 1:48
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closed as too localized by Qmechanic♦ Feb 15 at 15:29

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1 Answer

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Assume the relative speed of the block to be $v_r$. Write equations for momentum to find $v_A$. Replace $v_r $ with $-v_r$. Done.

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Please accept my applogies. I seem to be making a lot of stupid mistakes tonight. Another comment edit... – dmckee♦ Mar 14 '12 at 1:51
@dmckee No problem! Superpings, comment editing, and exotic buttons... You guys are SE ninjas! =D – Manishearth♦ Mar 14 '12 at 2:08

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