# Homework Help: What is the average force exerted by the plate on the ball

1. Nov 27, 2007

### mkwok

1. The problem statement, all variables and given/known data
A 4.00 kg steel ball is dropped onto a copper plate from a height of 10.0 m. If the ball leaves a dent 2.75 mm deep, what is the average force exerted by the plate on the ball during the impact?

2. Relevant equations
KE=1/2mv^2
F=ma
Wgrav=mgh

3. The attempt at a solution

when the ball hit the plate, the ball is traveling at a speed of 2ax, which is also 196m/s
so the Kinetic Energy would be 76832 the moment the ball hits the plate

since W=Fd, so 76832=F(2.75/1000)
F=27938909.1N

just looking by the numbers, I can tell this is wrong

2. Nov 27, 2007

### rock.freak667

Ignoring air resistance..all the gravitational potential energy is converted into kinetic energy as the mass falls...when the ball hits the copper plate, the work done in moving the ball 2.75mm into the copper. so that basically the loss in k.e. is equal to the work done in moving it into the copper
$W=Fs$ so that $mgh=Fs$