# Homework Help: Loss of energy

1. Oct 9, 2009

### Amel

Ok so the rpoblem is A 2.20kg box slides down a rough incline plane from a height h of 1.63m. The box had a speed of 2.33m/s at the top and a speed of 1.90m/s at the bottom. Calculate the mechanical energy lost due to friction (as heat, etc.).

and im not sure where to even begin with this one. its my last problem I need to finish.

2. Oct 9, 2009

### mgb_phys

At the top you have kinetic energy and potential energy.
At the bottom you have kinetic energy.
The difference is energy lost to friction

hint work (energy) = force * distance

3. Oct 9, 2009

### Amel

So do you do (1/2)mv^2 for both speeds? and find the difference?

or do you use mgh= PE

4. Oct 9, 2009

### Amel

Ok thanks I got it right.

5. Oct 9, 2009

### mgb_phys

Both
do the 1/2 mv^2 for the KE at each end, then take off the 'mgh' the stuff that's left must have gone to friction

6. Oct 9, 2009

### Amel

Yeah I got it. mgh is PE and .5mv^2 is KE at the top then you have .5mv^2 at the bottom and find the difference. got 3.72e+01 J. and it was right.