Question

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

Answer 1

Correct Answer - B
It can be observed from figure that `P` and `Q` shall collide if the initial component of velocity of `P` along incline. `u_(||) =0` that is particle is projected perpendicular to incline.

`:. ` Time of flight `T=(2mu_|_)/(gcos theta)=(2u)/(gcos theta)`
`:. u=(gTcos theta)/(2)=10m//s`