Question

A car slams on the brakes to stop. The road pushes back up on the car with a normal force of 12,750 N and friction from the brakes provides 9,560 N of force to stop the car. Calculate the coefficient of friction between the brakes and the wheels.

Answer 1

Answer:

$\displaystyle \mu_d=0.75$

Explanation:

Coefficients of Friction

Objects in physical contact produce friction which usually manifests as thermal energy being dissipated in the surface where the objects are interacting. It's usually harder to start to move an object from rest, that keeps moving it at a constant speed on the same surface. That is why there are two different coefficients of friction: the static and the dynamic. As mentioned, the static coefficient $\mu_s$ is greater than the dynamic coefficient $\mu_d$. The car is already moving and is attempting to stop. The coefficient of friction is defined as

$\displaystyle \mu_d=\frac{F_r}{N}$

Where Fr is the force of friction and N is the normal or the force the road pushes back up on the car. With the given data, we have

$\displaystyle \mu_d=\frac{9,560\ N}{12,750\ N}$

$\displaystyle \boxed{\mu_d=0.75}$

The coefficient of friction is dimensionless (doesn't have any units)