# Homework Help: Change in the momentum problem

1. Mar 29, 2005

### Honore

QUESTION:
"A 10-m-long glider with a mass of 680 kg (including the passengers) is gliding horizontally through the air at when a 60 kg skydiver drops out by releasing his grip on the glider. What is the glider's speed just after the skydiver lets go?"

My problem here is that I do not understand what this problem is got to do with the length of the glider since the force is not asked, nor it does not seem to be needed.

My solution is based on the change in the momentum: m1*v1 = m2*v2 and 680kg * 30m/s = (680-60)kg * v2 and I find v2=32.9m/s and our on-line system says it is incorrect. What's wrong/missing in my solution?

Thanks.

2. Mar 29, 2005

### StatusX

Your method is wrong because the momentum of the whole system must be conserverd, including the skydiver. But I don't see why the velocity should change. Ignoring air resistance, and if the skydiver just jumps straight down without pushing off in one direction, he would continue moving forward at the same horizontal velocity, while only his vertical velocity would change (only horizontal momentum is conserved here because of gravity). So the total horizontal momentum will only be the same if the glider continues at its speed as well.

3. Mar 29, 2005

### Honore

Thank you. The fact that the velocity of the glider should not change seems right after your explanation.