4. A car of mass 2000 kg is traveling at 45 m/s when the driver spots a policeman anead. i ne univer apprivo

the brakes lightly for 3.0 seconds until he slows down below the speed limit. If the average force applied

by the brakes was 1.4 X 104 N, by how much did the kinetic energy of the car change?

The change in the Kinetic Energy of the car, E = 1449000 joules

Explanation:

Given,

The mass of the car, m = 2000 Kg

The speed of the car, v = 45 m/s

The brake applied on the car for a duration, t = 3 s

The average force applied by the brake, F = 1.4 x 10⁴ N

The kinetic energy of the body is given by the relation,

K. E = 1/2 mv²

The initial kinetic energy of the car,

K. E = 0.5 x 2000 x 45

= 2025000 J

The force applied by the brakes

F = m x a

Therefore, the deceleration of the car

a = F / m

= 1.4 x 10⁴ / 2000

= 7 m/s²

Using the first equations of motion,

v = u + at

v = 45 + (-7) (3) ∵ (-7) car is decelerating

v = 24 m/s

The final kinetic energy of the car

k. e = 0.5 x 2000 x 24

= 576000 J

The difference in the kinetic energy,

E = K. E - k. e

= 2025000 J - 576000 J

= 1449000 joules

Hence, the change in the Kinetic Energy of the car, E = 1449000 joules