First slide
Collisions
Question

A body of mass m1  moving with a velocity 3 ms–1 collides with another body at rest of mass m2. After collision the velocities of the two bodies are 2 ms–1 and 5ms–1 respectively along the direction of motion of  m1. The ratio m1 / m2  is

Moderate
Solution

If target is at rest then final velocity of bodies are 
v1=m1m2m1+m2u1   …(i) and v2=2m1u1m1+m2   …(ii)
From (i) and (ii)  v1v2=m1m22m1=25m1m2=5 

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