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`. If the collision is elastic their respective final velocities are

Options

A. `63 cm//s,144 cm//s`
B. `144 cm//s, 63 cm//s`
C. `19 cm//s, 100 cm//s`
D. `100 cm//s, 19 cm//s`

Answer

B

Explanation

As mass, `m = rho(volume) = rho (4)/(3) pi r^(3)`
`m alpha r^(3)` so, `v_(1)=((r_(1)^(3) -r_(2)^(3))/(r_(1)^(3)+r_(2)^(3))) u_(1)` and `v_(2) = (2 r_(1)^(3) u_(1))/(r_(1)^(3) + r_(2)^(3))`.