Question

How much work is to be done to increase the velocity of a car from 18 kmh-1 to 72 kmh-1, if the mass of the car is 2000 kg?

Answer 1

Answer:

Work Done = The Change in Kinetic Energy

= 1/2mv2 - 1/2 mu2

The Mass of car = 2000 kg

Initial Velocity = 18 km/h

= 18 * 5 / 18

= 5

= 5 m/s

Final Velocity = 72 km/hr

= 72 * 5/18

= 5 * 4

= 20 m/s

Work Done = 1/2 mv2 - 1/2 mu2

= 1/2 m(v2 - u2)

= 1/2 * 2000 ( 20 * 20 - 5 * 5)

= 1000 ( 400 - 25)

= 1000 * 375

= 375000 J

Answer 2

Answer:

u = 18 km/h = 5 m/s

v = 72 km/h = 20 m/s

m = 2000 kg

Initial kinetic energy = 1/2*2000*(5)^2 = 25000 J

Final kinetic energy = 1/2*2000*(20)^2 = 400000 J

Work done = Change in KE = 400000 - 25000 = 375000 J