Coefficient of Friction between tires and racetrack

[pech0706]

Homework Statement

Jeff Gordon (a race-car driver) discovers that he can accelerate at 4.0m/s² without spinning his tires, but if he tries to accelerate more rapidly he always "burns rubber."
Find the coefficient of friction between his tires and the road. Assume the force from the engine is applied only to the rear tires.

Homework Equations

F_friction=$$\mu$$_kN
$$E$$=V+F_friction

The Attempt at a Solution

I don't even know where to begin on this

 

[tiny-tim]

welcome to pf!

hi pech0706! welcome to pf!

(have a mu: µ )

only external forces can move the car

the only (horizontal) external force is the friction from the road on the back tyres * …

so how much is this friction force when a = 4.0 m/s ?

(call the mass of the car "m")

* EDIT: come to think of it, that's not quite true …

when the car is accelerating, there's a small backward friction force from the road on the front tyres, essentially caused by the inertia of the front tyres: but I think you're meant to ignore that!