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Grade: 12th pass
Ball falls from height strikes  floor of lift with velocity 10 if the lift moves upward with velocity 1m/s find the velocity with which the ball rebounds 
4 months ago

Answers : (2)

Vikas TU
9814 Points
Dear student 
since the lift is moving upward in the given problem, u1 is positive (+10 m/s)and u2 is negative(-1 m/s)
For elastic collision
solving these two equations, we may get
since the lift is moving upward
V1 =(-m2*10+2m2*(-1))/m2
So that V1= -12 m/s
4 months ago
23389 Points
We consider initial velocity of the ball as u1=-10 m/s with reference to ground, We have taken downward direction as negative. The initial velocity of lift is u2=1m/s. After the collision let the velocities be v1 and v2. Since collision is elastic ,the coefficient of restitution e=1. 
Then,  1=(v1-v2)/(u2-u1) or u2-u1=v1-v2. Putting values of u1 and u2 and taking v2=u2 as lift is very heavy, we have ,  v1=2+10=12m/s for observer on ground.
For observer in the lift the lift is stationary and velocity of the ball before and after collision has same value with reversed direction . So, answer for that observer will be 10 m/
4 months ago
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