Asked by Shauna

A wagon is coasting at a speed, vA, along a straight and level road. When ten percent 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, vB. Calculate the ratio of vB/vA.
Answered by Damon
m and .1 m

original momentum
= m VA

momentum remains m Va throiughout
so
m Va = .1 m (Va+V)
and
m Va = .1 m (Va-V) + .9 m Vb
so
.1 m Va+.1 m V = .1 m Va-.1 m V+.9 m Vb
.2 m V = .9 m Vb
so
V = 4.5 Vb
but
m Va = .1 m Va + .1 m V
so
V = 9 Va
so
9 Va = 4.5 Vb
Vb/Va = 2


Answered by David
No, youa are wrong. It is not

mVa = .1m(Va-V) + .9mVb

it is

mVa = (-).1m(Va+V) + .9mVb

it is not 2, it is 20/9
Answered by shiv
Damon is absolutely right!
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