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

Answer

B

Explanation

It can be observed from figure that `P` and `Q` shall collide if the initial component of velocity `P` on inclined plane i.e. along incline `u=0` that is particle is projected perpendicular to incline.
`:.` Time of ligh `T=(2u)/(g cos theta):. u=(gT cos theta)/2=10 m//s`