A wooden block of mass `10 gm` is dropped from the top of a cliff `100 m` high. Simultaneously a bullet of same mass is fired from the foot of the cliff vertically upwards with a velocity of `100 ms^(-1)`. If the bullet after collision gets embedded in the block, the common velocity of the bullet and the block immediately after collision is `(g=10 ms^(-2))`.

Options

A. `40 ms^(-1)` downward
B. `40 ms^(-1)` upward
C. `80 ms^(-1)` upward
D. zero

Answer

B

Explanation

Time after which collision takes place`t = (h)/(u)` before collsion, initial velocity of the wooden block `u_(1) = u-g t`
`rArr m_(1)u_(1) -m_(2)u_(2) = (m_(1) + m_(2)) v`.