A ball is projected from the ground at an angle θ  with the horizontal. After 1 second it is moving at an angle 450  with the horizontal and after 2 seconds it is moving horizontally. What is the velocity of projection of the ball?

Suppose the angle made by the instantaneous velocity with the horizontal be α . Then tanα=vyvx=usinθ−gtucosθ Given that, α=450 , when t=1 sec α=00 , when t=2 sec This gives, ucosθ=usinθ−g usinθ−2g=0 Solving we find, usinθ=2g ucosθ=g Solving we get, u=5 g=105ms−1