Question

the brakes on a car do 240,000 j of work in stopping a car. if the car travels a disance of 40 m while the brakes are being applied, how large is the average force that the brakes exert on the car?

Answer 1

Given:

The brakes on a car do 240,000 j of work in stopping a car. The car travels a distance of 40 m before stopping.

To find:

Value of average force ?

Calculation:

• The work done by a force is equal to the magnitude of force and displacement of the object.

• Let the force be F :

$\therefore \: work = F \times d \times \cos( {180}^{ \circ} )$

• Angle will be 180° , because the retarding force is opposite to the displacement.

$\implies \: 240000 = F \times 40 \times ( - 1)$

$\implies \: - 240000 = F \times 40$

$\implies \: F = - 6000 \: N$

So, the force applied is -6000 N.