Question

A particle is projected from the ground at an angle theeta with the horizontal with an initial speed u .The time after which the velocity vector of projectile is perpendicular to the initial velocity is
1- u/gcostheeta
2-u/gsintheeta
3-usintheeta/g
4-2usintheeta/g

Answer 1

Please refer the attachment

It’s a bit confusing but look at the figure carefully and try to understand

Hope it helps :)

Answer 2

Answer:

theeta=∅

option 3 is right = usin∅/g