# Work Done by Air Resistance on rain drops

1. Nov 5, 2007

### grouchy

1. The problem statement, all variables and given/known data

A 2.76 x 10^-5 kg raindrop falls vertically at constant speed under the influence of gravity and air resistance. After the drop has fallen 131m, what is the work done by gravity? After J is found for gravity, what is the work done by air resistance in units of J.

2. Relevant equations

W = FD

3. The attempt at a solution

I got the work done by gravity W = (mg)*d. so that W is 0.03543288 J. But I have no idea where to start with the air resistance...

2. Nov 5, 2007

### grouchy

nvm, got the answer. its the opposite of the work of gravity since the speed is constant

3. Nov 5, 2007

### HallsofIvy

Staff Emeritus
Since the rain drop falls at a constant speed, the upward force of air resistance must be exactly the same as the force of gravity.

Take a look at "work done by gravity"? If there were no air resistance, the loss in potential energy, (mg)d, would go into increased kinetic energy. But here, because the speed is constant there is no increase in kinetic energy. Where do you think all that loss of potential energy goes?