The average rate of acceleration for a breaking car was -12.2m/s2. If the car had a mass of 925 kg, find the frictional force and direction. a = -12.2m/s2 m = 925 kg Fn = 9074.25 N This is what I've figured out. I don't know how to find the coefficient of friction. If I get the coefficient I think I can multiply it by the normal force to get the frictional force.