# Ellastic collision w/rebound

1. Jan 2, 2012

### canicon25

1. The problem statement, all variables and given/known data

A 150 kg cart moving at 13 m/s east collided with a 420 kg wagon moving at 5.0 m/s east.
The cart rebounded westward with a speed of 3.0 m/s . What was the speed of the wagon after the collision? Observe standard Cartesian coordinates.

2. Relevant equations

KE1+KE2=KE1'+KE2'
conservation of momentum
conservation of kinetic energy in elastic collisions

3. The attempt at a solution
(0.5)(150)(13)2+(0.5)(420)(5)2=(0.5)(150)(-3)2+(0.5)(420)v2
v=9.0m/s

Last edited: Jan 2, 2012
2. Jan 2, 2012

### issacnewton

the problem itself doesn't say that the collision is elastic. so just use conservation of momentum here.

3. Jan 2, 2012

### cupid.callin

issacnewton is right !!!
Conservation of kinetic energy is valid only when coefficient of restitution(e) is 1
here its not specified, so you must use momentum conservation.

ALSO:
if e is given and is ≠1 then you may use:
(v2 - v1) = e(u1 - u2)