# Impact Force Problem

1. Feb 27, 2007

### gonefishing

When dropping a metal ball onto a foam mat what is the formula for the impact speed. I know the impact speed, rebound speed, the mass of the ball and time of the ball on the mat.

I know:

F = m[delta]v
.......[delta]t

and

F = mg , where g= -9.8 N/kg

But what is the impact force?

Is it F = m[delta]v + mg ?
.............[delta]t

2. Feb 27, 2007

### Axiom_137

Force

$$F = \frac{d\rho}{dt}$$

(Does my LaTeX work?)

3. Feb 27, 2007

### gonefishing

ok, but still I don't understand whether the weight force affects the value of the impact force.

The ball is being dropped vertically, so do we add the weight force to dp/dt?

4. Feb 27, 2007

### PhanthomJay

When you calculate the momentum change over time, you are calculating the NET force acting on the object, per Newton's 2nd law. The net force is a combination of the gravity force downward and the normal force upward. So, what does that tell you about the 'impact' (normal) force?