How Does Bending Knees Reduce Impact Force in a Jump?

[CaptFormal]

Homework Statement

When jumping straight down, you can be seriously injured if you land stiff-legged. One way to avoid injury is to bend your knees upon landing to reduce the force of the impact. A 72.6 kg man just before contact with the ground has a speed of 6.35 m/s. In a stiff-legged landing he comes to a halt in 2.19 ms. Calculate the average net force that acts on him during this time.

Homework Equations

The Attempt at a Solution

I don't even know how to start this one. Please help.

 

[willem2]

what is the average acceleration?

F=ma

 

[CaptFormal]

I don't know. How would you go about solving for it?

 

[willem2]

Average acceleration is $$\Delta v / \Delta t$$