A particle P is projected from a point on the surface of smooth inclined plane (see figure). Simultaneously another particle Q is released on the smooth inclined plane from the same position. P and Q collide after`t=4`. The speed of projection of P is

Options

A. 5m/s
B. 10m/s
C. 15m/s
D. 20m/s

Answer

d

Explanation

It can be obseved from figure that P and Q shall collide if the initial component of velocity 'P' on inclined plane i.e., along incline u=0i.e., particle is p rojected perpendicu lar to incline.
`therefore` Time of light `t_(AB)=(u sin theta)/(g)`
(time to reach the maximum height of projectile) particle rebound with `u cos theta` in vertical direction (as collision is elastic ).
Time required to reach maximum height
`=t_(AB)+t_(BC)=(u sin theta)/(g)+(u cos theta)/(g)`