# HELP Projectile motion and Force puzzler

#### paigegail

HELP!! Projectile motion and Force puzzler!!

A 10.8 kg box is 5.0 m from the edge of a 12.96 m high cliff. Bob pushes the box over the edge of the cliff by applying a constant horizontal force to it until the box goes over the edge. The force of friction on the box is 49.0 N and the box lands 7.5 m from the base of the cliff. How much force did Bob apply to the box while he was pushing?

What am i supposed to do... I know I'm supposed to work backwards...which is what I did. I found the velocities in the vertical and horizontal directions...what do I do now?!

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#### gnome

If you know the velocity (horizontal) of the box right at the edge of the cliff, the next step is to solve for the NET force that had to be applied constantly over a distance of 5 m to accelerate it from rest up to that velocity.

You are given the force of friction, which was a constant force acting in the opposite direction, so how much force did Bob apply?

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