# Homework Help: Coefficient of Static Friction with Acceleration

1. Mar 1, 2012

### PeachBanana

1. The problem statement, all variables and given/known data

A car can decelerate at -4.90 m/s^2 without skidding when coming to rest on a level road.
What would its deceleration be if the road were inclined at 11° uphill? Assume the same static friction coefficient.

2. Relevant equations

Force of Static Friction / Normal Force = coefficient of static friction
F (normal) - mg *sin 11° = 0

3. The attempt at a solution

(4.90m/s^2)/(9.8 m/s^2) = 0.5

I didn't know the mass so I just left it out.
F - mg *sin 11° = 0
F (normal) = mg * sin 11°
F = (9.8 m/s^2) * sin 11°
Normal force = 1.86 m/s^2

I know those are acceleration units so something more than likely went wrong there.

Force of static friction = (0.5)(1.86 m/s^2)
Force of Static Friction = 0.93 m/s^2

2. Mar 1, 2012

### Staff: Mentor

I don't understand this equation.
Good.

To find the acceleration, use ƩF = ma. What's the net force when going uphill?

(Hint: What are the parallel and perpendicular components of the weight?)

3. Mar 1, 2012

### PeachBanana

Doc Al - Sorry, the first one was a little unclear. I was attempting to find the normal force by saying the normal force equals the y component of the weight because there is no acceleration in the "y" direction. I think I should have used cosine instead of sine. Thank you for your advice.

4. Mar 1, 2012

Exactly.