A 20 kg ball moving with a velocity 6 m/s collides with a 30 kg ball initially at rest. If both of them coalesce, then the final velocity of the combined mass is :

Options

A. 6 m/s
B. 5 m/s
C. 3.6 m/s
D. 2.4 m/s

Answer

D

Explanation

From conservation of momentum.
Momentum before collision = Momentum after collision
`" "m_(1)u_(1)+m_(2)u_(2)=m_(1)v_(1)+m_(2)v_(2)`
`rArr" "20 times 6=50v`
`rArr" "v=120/50=2.4m//s`