Finding average resistive force

[jman1209]

I really need help with this!

Homework Statement

A 70-kg diver steps off a 10-m tower and drops from rest strait down into the water. If he comes to rest 5.0 m beneath the surface, determine the average resistive force exerted on him by the water.

Homework Equations

This is the only equation that I know goes with this problem:
(KE + PE_g + PE_s)_i = (KE + PE_g + PE_s)_f

The Attempt at a Solution

I can't get anywhere with this.

 

[gneill]

What's the diver's KE when he hits the water? What's his KE when he comes to a stop? How much work was done stopping him? How do you calculate work?