A steel ball of radius `2 cm` is initially at rest. It is struck head on by another stell ball of radius `4 cm` travelling with a velocity of `81 cm//s`. The common velocity if it is perfectly inelastic collision.

Options

A. `144 cm//s`
B. `61 cm//s`
C. `81 cm//s`
D. `72 cm//s`

Answer

D

Explanation

`r_(1)^(3)u_(1) +r_(2)^(3) u_(2)=(r_(1)^(3)+r_(2)^(3)) v{because m alpha r^(3)}`.