Collisions and changing frame of reference?

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collisions and "changing frame of reference?"

1. Homework Statement
A 6.0Kg trolley moving at 6.0 m/s right overtakes and collies with a 2kg trolley moving 2m/s right in the same direction on the same track. The collision is cushioned by a perfectly elastic bumper attached to one of the trolleys.

A) what is the speed and direction of each trolley after the collision?

B) What is the maximum amount of potential energy stored in the bumper during the collision?

2. Homework Equations
V1' = v1 (m1 - m2) / ( m1 + m2 )

V2f = 2*m1v1 / (m1+m2)

3. The Attempt at a Solution

for A) I tried that by substituting in values from the question and It gave me 3m/s and 9m/s... yet the answer says 4m/s and 8 m/s... am I doing anything wrong? =/

**my friend said something about change frame of reference...**

didn't start B yet because I didn't get A yet =/

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twenty5

Re: collisions and "changing frame of reference?"

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