Question

A 1000 kg car is moving with a constant speed. It is being pushed with 3000 N of force. Find the coefficient of kinetic friction, k. (Hint: You should find the acceleration of the car first so you can find the net force).

Answer 1

The acceleration of the car can be given as,

$a=\frac{F}{m}$

Plug in the known values,

$\begin{gathered} a=\frac{3000\text{ N}}{1000\text{ kg}}(\frac{1kgm/s^2}{1\text{ N}})_{} \\ =3m/s^2 \end{gathered}$

The net force which acts on the car is,

$F=ma$

The frictional force acting on the car is,

$f=\mu_kmg$

The net force is balanced by the frictional force which can be solved as,

$\begin{gathered} \mu_kmg=ma \\ \mu_k=\frac{a}{g} \end{gathered}$

Substitute the known values,

$\begin{gathered} \mu_k=\frac{3m/s^2}{9.8m/s^2} \\ =0.306 \end{gathered}$

Thus, the coefficient of kinetic friction is 0.306.