Question
A body P moving with velocity 10m/s strikes elastically with another body Q moving in the opposite direction with speed 12m/s. The body P after collision rebounds with velocity 9m/s. Find the velocity of Q.
Solution
Given,
Velocity of body P, 
,
Velocity of body Q, 
Velocity of body P, 
,
Velocity of body Q, 
= ?
We know that relative velocity of approach is equal to relative velocity of separation,
i.e. 
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That is,
