Question

A mass of 600 KG moving at 65 m/s begins breaking and skids on a slick pavement. Draw  the free body diagram for the car. if the car comes to a stop in 140 m what is the coefficient of kinetic friction between the tires and the road?

Answer 1

we need to find deceleration of the car.

The final velocity (v) is zero.

The initial velocity (u) is 65 m/s

so,

v² - u² = 2ad

0² - 65² = 2 * a * 140

a = - 15.089 m/s²

--------

equating forces in horizontal direction

F_net = ma

0 - F_k = 600 * - 15.089

F_k = 9053.57 N

this is the force of kinetic friction

Now, we know

F_k = u_k N

F_k = u_k mg

u_k = 9053.57 / 600 * 9.8

u_k = 1.54

(Don't be surprised if value is more than 1, the pavement is oily ( slick) , so it is possible)

-----------------------------------------------------------------------------