Coefficient of kinetic Friction given velocity and distance.

[pech0706]

Homework Statement

A car is moving with a velocity of 20m/s when the brakes are applied and the wheels lock (stop spinning), The car then slides to a stop in 40m. FInd the coefficient of kinitic friction between the tires and the road.

Homework Equations

F=ma
Ffriction=coefficient fo friction*N
N=mg

The Attempt at a Solution

I have drawn a picture and free body diagram, but that's as far as I've gotten. I'm stuck because I don't know how to calculate the normal force without the mass, and I don't now how to find the coefficient without N. I know the answer is 0.51, but I do not know how to get there.

 

[cupid.callin]

dont worry about mass.
take it as m
it will get canceled in the process.

 

[pech0706]

So, basically that means the total force acting on the car is the velocity and the frictional force. After ignoring the mass though, I'm still stuck. I don't know how to find the frictional force or the coefficient of friciton when ignoring mass.

 

[cupid.callin]

Dont ignore mass, take it as m.

Then do the general method and find the answer.
mass won't be any problem