After perfectly inelastic collision between two identical particles moving with same speed in different directions, the speed of the combined particle becomes half the initial speed of either particle. The angle between the velocities of the two before collision is

Explanation

In perfectly inelastic collision between two particles, linear momentum is converved. Let `theta` be the angle between the velocities of the two particles before collision. Then `p^(2)= p_(1)^(2) + p_(2)^(2) + 2p_(1) p_(2) cos theta`
or `(2m (v)/(2))^(2)= (mv)^(2) + (mv)^(2) + 2(mv) (mv) cos theta` or `1= 1 + 1+ 2 cos theta or cos theta = - (1)/(2), (or) theta= 120^(@)`