It is given that the projectile passes through (20,10) and angle of projection is θ=45∘. Using the trajectory equation,
y=xtanθ−2u2cos2θgx2
⇒10=20−u2(10)(100)
⇒u=20ms−1
Now the time of flight of projectile,
T=g2usinθ
⇒T=2(10)(2)(20)=22s⇒2T=2s
Now velocity of the projectile at any time t can be written as,
v=ucosθi^+(usinθ−gt)j^
⇒v=102i^+(102−10(2)]j^ms−1
Therefore, momentum p=Mv=1002i^+(1002−200)j^Ns