# Homework Help: Conservation of motion

1. Oct 15, 2009

### Chuck 86

1. The problem statement, all variables and given/known data
boy in a wheelchair (total mass, 48.7 kg) wins a race with a skateboarder. He has a speed of 1.23 m/s at the crest of a slope 2.37 m high and 14.0 m long. At the bottom of the slope, his speed is 6.27 m/s. If air resistance and rolling resistance can be modeled as a constant frictional force of 41.8 N, calculate the work he did in pushing forward on his wheels during the downhill ride.

2. Relevant equations
Ei-Ef=Wfriction+Woutside forces

1/2mv^2, mgh
3. The attempt at a solution
cant seem to set this up right. dont know the equations for the 2 work

2. Oct 15, 2009

### Donaldos

Can't you think of a general expression for work that you could use here?

3. Oct 15, 2009

### Chuck 86

Not of the outside forces

4. Oct 15, 2009

### Chuck 86

that would be cool to get some help instead of pointing out that im not smart, thats why im asking for help

5. Oct 16, 2009

### Donaldos

What are the outside forces?

In particular, what is the work done by gravity?

6. Oct 16, 2009

### Chuck 86

MgH=(48.7)(9.8)(14)

7. Oct 16, 2009

### Donaldos

OK but H=2.37 m here, not 14m.

Now you just need to calculate the work done by friction.