A car weighing 14

Mass of the car, m = 1400 kg

Height covered by the car, h = 10 m

Work done on the car by gravity = -mgh

= -1400×9.8×10

= -137200

(negative sign indicates that the displacement is opposite to the gravitational force)

Initially, speed of the car = 54 km/h = 15 m/s

Initial kinetic energy of the car at given speed = 1/2 × mass × (speed of the car)²

= 0.5 × 1400 × 15 × 15

= 157500 J

Final kinetic energy of the car (it eventually stops) = 0 m/s

Change in kinetic energy of the car = 0 – 157500 = - 157500 J

Also, this change in kinetic energy of the car = Work done by friction + work done by gravity

⇒ Work done by friction = Change in kinetic energy – work done by gravity

= -157500 – (-137200)

= -157500 + 137200

= -20300 J

⇒ Work done against friction = 20300 J