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### Best Answer Ben Evans says

There are several assumptions. The first is that when the ball hits the ground it does not have its velocity translated into rotational motion. The vertical component of the velocity would make an inelastic collision with the ground. It also needs to also not roll from the point of impact. Without the first two assumptions, it would be impossible to solve without defining these. Without the third assumption the ball would not stop.

.21mgd=1/2m(Vx)^2 or Vx={(.42)(9.8)}^1/2=2 m/s

At a 45 degree angle that would mean the Vy=2 m/s

We know Vy we know g but we don't know time nor distance so we will use this equation:

Vyf^2-Vyi^2=2gh

The initial velocity in the y direction is 0 therefore h=4/{(2)(9.8)}=0.20 m

Great answer and explanation!