# Homework Help: Impulse Problem

1. Oct 14, 2004

### koomba

Hey I've been having trouble with this impulse problem, in fact I don't even seem to know where to start. My prof didn't even cover any impulse problems in class and then expects us to do one for homework. But anyways, any help would be appreciated, I'm sure theres someone who can help me. Here you go:

A bungee jumper (m = 63.00kg) tied to a 41.00m cord, leaps off a 71.00m tall bridge. He falls to 8.00m above the water before the bungee cord pulls him back up. What size impulse is exerted on the bungee jumper while the cord stretches.

Thanks!

2. Oct 14, 2004

### Staff: Mentor

When a force is exerted on something for an amount of time an impulse is imparted to the object. The "impulse" = force X time = the change in momentum. So, find the change in momentum of the bungee jumper starting with the point where the cord begins to stretch.

Hint: What's the initial momentum of the jumper at the moment the cord starts to stretch?

Last edited: Oct 14, 2004
3. Oct 14, 2004

### arildno

Note that whatever the stiffness of the cord, the force exerted on you by the cord is a CONSERVATIVE force.
What does this tell you about the relation between:
1)Your velocity just before the bungee cord become stretched beyond its rest length.
2)Your velocity just after the bungee cord regains its rest length.

3)Then, how can you compute 1) (and from it, 2).
4) What must then the impulse from the cord be?

4. Oct 14, 2004

### arildno

I would like to point out, that a fundamental assumption must be made:
That the time interval during which the cord is stretched must be relatively short.
(The impulse from the force of gravity must be negligible compared to the other terms)

5. Oct 14, 2004

### Staff: Mentor

I don't think one needs to make that assumption, given the way the problem is phrased: the problem asks for the impulse on the jumper, not necessarily the impulse from the cord alone.