A ball of mass m moving with a velocity v hits a massive wall moving towards the ball with a velocity u. An elastic impact lasts for a time Δ t
A
The average elastic force acting on the ball is 
B
The average elastic force acting on the ball is 
C
The kinetic energy of the ball increases by 2mu (u + v)
D
The kinetic energy of the ball remains the same after the collision.
Text Solution
Verified by ExpertsThe correct answer is:
CHECK THE SOLUTION.
(b, c)
u 1 = v v 2 = – (v + 2u) e = 1.
|N.dt| = m (v 1 – u 1 )
N.dt = m (+v + 2u + v)
N.dt = 2m (u + v).
N = 
u 1 = v v 1 = 2u + v
Δ k = 
mv 1 2 – 
mu 1 2 = 
[m (2u + v) 2 – v 2 ] = 
[4u 2 + v 2 + 4uv – v 2 ] = 2mu (u + v)
By energy conservation
mv 2 + 0 = (2m) + kx 2
at maximum compression k = (m+m)v 2 Since final velocity of ball is 2 (u + v), its K.E. increases
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