Homework Help: GRE question - Work-KE theorem?

1. Aug 28, 2009

1. The problem statement, all variables and given/known data
A 5-kilogram stone is dropped on a nail and drives the nail 0.025 meter into a piece of wood. If the stone is moving at 10 meters per second when it hits the nail, the average force exerted on the nail by the stone while the nail is going into the wood is most nearly

A) 10 N
B) 100 N
C) 1000 N
D) 10000 N
E) 100000 N

2. Relevant equations
W = delta K

3. The attempt at a solution
I've used kinematics to find the answer to this problem (choice D), but that assumes that the acceleration is constant, which I don't think we can do.

Is there a way to apply the work-KE theorem? I know energy cannot be conserved because there is energy dissipated while the nail is driven into the wood.

Thanks for any help.

2. Aug 28, 2009

nnnm4

I get the answer you do (D). You don't assume that acceleration is constant, you're finding the AVERAGE force, so it's effectively asking for a constant force.