# Mechanical energy and velocity

1. Nov 23, 2008

### bkl4life

1. The problem statement, all variables and given/known data
A 60 kg skier slides from rest down a 30 m slope that makes an angle of 26 degrees with the horizontal. Assume the coefficient of friction of the slope is .2.

How much mechanical energy does the skier lose while skiing down the hill?
What is the velocity of the skier lose while skiing down the hill?

2. Relevant equations

w=mgh

3. The attempt at a solution
m=(60)(9.8)(30)=17640 J

I'm not sure what to do after this.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Nov 23, 2008

### mgb_phys

H isn't 30m, the slope is 30m long (ie along the hypotonuse) you have to work out from the 26deg how high the slope is.

3. Nov 24, 2008

### bkl4life

Okay, so I do

(60)(9.8)(cos26)

Is it possible to take that answer and set it up to find the velocity? Do I need part A to find part B. I'm just really confused.

4. Nov 24, 2008

### mgb_phys

What units does 'mgh' have, what units does your equation have?
Always put in the units - it lets you spot mistakes.
The vertical height is 30 sin(26) m

You know how muhc potential energy the skier loses, and this equals the kinetic energy they gain less the frictional losses.
The energy lost to friction is force*distance, so the length of the slope * the frictional force along the slope

5. Nov 24, 2008

### bkl4life

Thanks! This makes sense. I always mess up my units!