# Homework Help: Girl slides down a slide. What is the friction?

1. Oct 20, 2008

### fallen186

1. The problem statement, all variables and given/known data
A 17 kg girl slides down a playground slide that is 2.7 m high. When she reaches the bottom of the slide, her speed is 1.3 m/s. What is the cohefficient of friction?

2. Relevant equations
F=ma

3. The attempt at a solution

I calculated the normal force to be 166.77 N (sin(theta)*m*g = sin(20)*17 kg*9.81 m/s^2 = 166.77 N)

I found distance of the slide by (Hyp = Opp/Sin(theta) = 2.7m /sin (20) = 7.89 m)

I then filled in the equation Vf^2 = Vi^2 + 2ad ( (1.3^2 = 0^2 + 2a *7.89m) = (1.69 = 15.788 a) = (a = .107m/s^2 )

I then used F=ma ((F = 17kg *.107m/s^2)= (F =1.82 N))

Then i used mew = 1.82N /166.77 N = .0109

.0109 is wrong. Ehhh how do i do this??!1qWsdf

2. Oct 20, 2008

### LowlyPion

How did you know it was 20 degrees?

Anyway figure how much potential energy she had at the top.

PE = m*g*h

Then how much KE does she have at the bottom? mV2/2

The difference is the work that went to friction. = u*m*g*cosθ*d

3. Oct 20, 2008

### fallen186

Thanks that helped a lot. And it was in the picture. Sorry bout that