# Objects in Incline problem

1. Feb 24, 2004

### RingWraith2086

OK here's the problem: An extremely light drivable car with a mass of only 9.50 kg was built. Suppose that the wheels of the car are locked, so that the car no longer rolls. If the car is pushed up a 30° slope by an applied for of 80.0 N, the net accel. of the car is 1.64 m/s2. What is the coefficient of kinetic friction between the car and the incline?

And where's what I've done:
m = 9.5
W = 93.195
a = 1.64
Fnet = ma = 15.58
Fapplied = 80
Ffriction = Fapplied - Fnet = 64.46
Fperendicular = CosTheta(W) = 80.709 (also Fnormal)
Fparallel = SinTheta(W) = 46.5975

Then I have:
Coeff of friction = Ffriction/Fnormal = 64.46/46.5975 = 1.3833

But according to the answers my teacher gave me, and logic (that seems a little bit high for the situation), that isn't right. Please show me where I'm going wrong. Thanks.

Last edited: Feb 24, 2004
2. Feb 24, 2004

### jamesrc

You forgot the component of the weight along the incline when calculating Fnet.

$$F_{\rm net} = F_{\rm applied} - F_{\rm parallel} - F_{\rm friction}$$

Try redoing it from there and see how it works out.

3. Feb 24, 2004

### RingWraith2086

This teacher is the best science teacher I've ever had, but for some reason she failed to mention that the Fparallel was in the Fnet formula on the angle. And I know I didn't just copy it down wrong, because two of my friends (one of whom made a 36 on the math part of his ACT) couldn't do it either. I'll ask her about it when I get back to school, but thanks for the help. I've got another one I need help on, but I'm gonna start a different thread. Thanks again.