Question

The speed of a car of mass 1000 kg is reduced from 20 m/s to 10 m/s. What is the work done by the brakes of the car?

• A. 150 kJ
• B. 120 kJ
• C. 100 kJ
• D. 80 k J

Answer 1

The correct option is A 150 kJ

Work done by the brakes of a car will be the net change in the kinetic energy of car
$W=\frac{1}{2}m({v_2}^2-{v_1}^2)$
$W=\frac{1}{2}m({10}^2-{20}^2)$
$W=\frac{1}{2}m(100-400)$$=$$\frac{1}{2}1000(-300)$
$W=-150000J=-150KJ$
Hence, option A is correct.