A body P of mass m moving along the positive x-direction with velocity u collides with a body of mass M initially at rest. After the collision body P moves along the positive y-direction and body Q moves along a direction making an angle `theta` below the x-axis. The collision is assumed to be elastic.
If `M = 2 m`, the kinetic energy gained by body Q due to collision is

Options

A. `2/3 m u^2`
B. `1/3 m u^2`
C. `1/2 m u^2`
D. `m u^2`

Answer

B

Explanation

Similarly we get `V = u/(sqrt3)` .Therefore the increase in KE of Q is
`1/2 MV^2 - 0 = 1/2 Mv^2 = 1/2 xx 2m xx (u/(sqrt3))^2 = 1/3 m u^2`