How to find coefficient of friction?

[Narayanswamy]

If a driver traveling down an 8% grade hill slams down the brakes of his car and skids 30 meters, what is the coefficient of friction ( assuming he was traveling at 25 MPH or more)?

Appreciate your help asap.

 

[fliinghier]

you use the acceleration due to gravity and say that the friction overcomes that by ___ amount

 

[Narayanswamy]

What is 8% gradient in degrees?

 

[Narayanswamy]

is Coefficient of friction tan(slope in degrees) ?

 

[fliinghier]

i believe that 8% is the tangent of the angle. the coefficient of friction is mu, and for most cars should be between .6 and .8

 

[Doc Al]

If a driver traveling down an 8% grade hill slams down the brakes of his car and skids 30 meters, what is the coefficient of friction ( assuming he was traveling at 25 MPH or more)?

Appreciate your help asap.

Assemble the usual suspects: Draw a diagram showing all the forces acting on the car. Apply Newton's 2nd law to relate the net force to the acceleration. Use kinematics or work/energy to compute the acceleration. (Pick a specific speed: convert 25 mph to m/s.)