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 = 2m`, the speed of body P after the collision will be

Options

A. `u/2`
B. `u/(sqrt2)`
C. `u/3`
D. `u/(sqrt3)`

Answer

D

Explanation

`M = 2m , ` then `sin theta = [(2m - m)/(2 xx 2m)]^(1//2) = 1/2 implies theta = 30^@`
Dividing eqn. (2) by eqn. (1) we get
`v = u tan theta = u tan(30^@) = u/(sqrt3)`