A block A of mass M moving with speed u collides elastically with block B of mass m which is connected to block C of mass m with a spring.

When the compression in spring is maximum, the velocity of block C with respect to block A is (Neglect the friction everywhere)

Options

A. zero
B. `(M/(M+m))u`
C. `(m/(M+m))u`
D. `(m/M)u`

Answer

B

Explanation

`v_(A) = (M-m)/(M+m) u and v_(B) = (2Mu)/(M+m)`
Velocity of C at maximum compression = `v_(B)/2`
`v_(c) = 1/2[(2M)/(M+m)]u = (M/(M+m))u`
`v_(CA) = v_(C)-v_(A) = (m/(M+m))u`