# Calculating Distance Using Force, Mass, and Acceleration

1. Nov 24, 2010

1. The problem statement, all variables and given/known data

A rock is dropped from x(meters) height. The rock weighs 68 kg, and its force at impact with the ground is 15 kilonewtons. If the acceleration due to gravity is 9.8m/s^2, what is the distance/height the rock has fallen?

2. Relevant equations

F=m*a

15kN=15000kg*m/s^2

666.4N=68kg*9.8m/s^2

The force exerted by the rock at stationary position is 666.4 Newtons.

The rock fall distance is x meters.

3. The attempt at a solution

666.4N*x=15000N

(666.4kg*m/s^2)*x=15000kg*m/s^2

x=(15000kg*m/s^2)/(666.4kg*m/s^2)

x=22.51

This was all I could come with, but it is simply the ratio of the force. How do I find distance?

Last edited: Nov 24, 2010
2. Nov 25, 2010

### Staff: Mentor

Please state the complete problem exactly as given. As you've written it, there's not enough information. (The impact force depends on the nature of the surface being hit.)

3. Nov 25, 2010

### AC130Nav

Shouldn't there be a formula for the kinetic energy of a mass falling distance x and a formula for the F generated by an unknown kinetic energy when it hits? The two could then be equated resolving x.

I don't see elastic/inelastic collisions mentioned.

4. Nov 25, 2010

### Staff: Mentor

That one's easy.