# How does a parachute help a man hit the ground with a small kinetic energy?

1. Dec 16, 2008

### hodgepodge

1. The problem statement, all variables and given/known data
How does a parachute help a man hit the ground with a small kinetic energy? Where does the energy go? Explain everything in energy terms.

2. Relevant equations

3. The attempt at a solution
i think that when the parachute is deployed, the kinetic energy the man has from falling is turned into potential energy, but where does the potential energy go? in the parachute? in the man?

2. Dec 16, 2008

### PhanthomJay

Well, no, when the chutist or skydiver jumos from the plane with chute not opened, he has a pretty high speed (lets just say 30m/s), which implies a high KE and also he has a high PE in relation to the ground. When he opens his chute, his speed drops radically, and so does his KE, and there's a slight PE drop as well as he gets a bit lower to the ground during chute deployment, but thta does not explain the KE loss. What force comes into play that causes him to lose his speed and do work to reduce that KE?

3. Dec 16, 2008

### hodgepodge

air resistance?

4. Dec 16, 2008

### PhanthomJay

Yes! The air drag force on the chute upwards counteracts the gravity force downward, acting to slow the descent and cause the loss of KE which is due to the work done by the drag force, per the applicable energy equations. But that loss doesn't get transferred to the man.
Now what little KE is left as he hits the ground, that gets lost also as his speed drops to 0, but i don't think that was what the problem was asking, as differnt forces come into play here during ground contact.

5. Dec 16, 2008

### hodgepodge

thank you very much