Help Physics Projectiles?

Question

In many locations, old abandoned stone quarries have become filled with water once excavating has been
completed. While standing on a quarry wall, a boy tosses a piece of granite into the water below. If he throws the rock horizontally with a velocity of 3.0 m/s and it strikes the water 4.5 m from the base of the wall, how high above the water is the wall?

Could somebody please help show me how to work this out? I am so lost.

Alright I figured out that time = 1.5s 
because D = VT
4.5m = 3.0 m/s * T
but where do I go from here?

? · Accepted Answer

It's initial horizontal velocity is 3 m/s. It's initial vertical velocity is 0. The horizontal velocity doesn't change (since we're assuming no air resistance), but the vertical velocity starts from rest and falls with an acceleration of 9.8m/s². The time it takes for it to travel 4.5 m is the same time it takes for it to fall a height of h.

h = ut + ½at² here u is the initial vertical velocity, u = 0

h = 0 + ½at²

h = 0.5(9.8)(1.5²)

h = ut + ½at²         here u is the initial vertical velocity, u = 0
h = 0 + ½at²
h = 0.5(9.8)(1.5²)

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Help Physics Projectiles?

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