Kinetic Energy and the Work-Kinetic Energy

[Joyci116]

Homework Statement

A 2100-kg pile driver is used to drive a steel I-beam into the ground. The pile driver falls 5.00 m before coming into contact with the top of the beam. Then it drives the beam 12.0 cm farther into the ground as it comes to rest. Using energy considerations, calculate the average force the beam exerts on the pile driver while the pile driver is brought to rest.

m=2100 kg
Xi=5.00m
Xf=12.0 cm =.12m

Homework Equations

K=.5mV^2
U=mgh
F=ma

The Attempt at a Solution

I rearranged the formula F=ma to a=F/m. And I tried using a kinematic equation, but I have failed.

 

[Spinnor]

I think you want to equate work with potential energy

F*x = F * (.12m) = mgh = mg(5m + .12m)

 

[Joyci116]

What I did is
Loss in energy=Loss in PE from the topmost point=mg(5.12)
Avg. Force=mg(5.12)/0.12
=8.78x10^5N

 

[Spinnor]

That is the number I get.

 

[Joyci116]

Thank you very much.