# Mechanical energy problem

1. Oct 25, 2007

### dbtarz

A projectile has a mass of .750kg and is shot straight up with an initial velocity of 18.0m/s. If the projectile rises to a max height of 11.8m, determine the magnitude of the average force due to air resistance. Can anyone help me with this?

2. Oct 25, 2007

### Galileo

The energy lost due to air resistance equals the work done by the air.

3. Oct 25, 2007

### dbtarz

I don't understand?

4. Oct 25, 2007

### Galileo

Suppose there is no air resistance. Can you calculate how high the projectile would go?

Given that, can you calculate the energy that is lost due to air resistance?

5. Oct 25, 2007

### Eolill

Drawing pictures and listing knowns/unknowns is great help. You know the mass, the height/displacement, and the velocity. These give you the initial kinetic energy and the final potential energy, and the initial energy is always equal to the final energy plus the work done by friction/air resistance/etc (the wasted energy).

It is all pretty straight-forward. ^^