Calculating Frictional Force on a Moving Car on a Slope

[draugrslayer]

Homework Statement

A 2,254-kg car is moving down a road with a slope of 10 degrees while speeding up at a rate of 1.1 m/s^2. What is the direction and magnitude of the frictional force?
(define positive in the forward direction, i.e., down the slope)?

Homework Equations

ax=μgcos-gsin

The Attempt at a Solution

μ=ax/gcos-gsin 1.1m/9.81(cos10-sin10)=0.138 i keep on getting this answer.

 

[Hypersphere]

I think it would be useful if you provided more details about your attempt. For starters, what does the free body diagram look like?