Two particles of equal masses moving with same momentum collide perfectly in-elastically. After the collision the combined mass moves with half of the speed of the individual masses. The angle between the initial momenta of individual particle is

Options

A. `60^(@)`
B. `90^(@)`
C. `120^(@)`
D. `45^(@)`

Answer

C

Explanation

As `|vecP_(1)|=|vecP_(2)|=|vecP|=P_(0)` (say), `vecP` is final momentum from conservation of linear momentum
`vecP_(1)+vecP_(2)=vecP:.P=sqrt(P_(1)^(2)+P_(2)^(2)+2P_(1)P_(2)costheta)`
or `P=sqrt(P^(2)+P^(2)+2P^(2)costheta)`
`:. costheta=(-1)/2impliestheta=120^(@)`