What is the work to be done to increase the velocity of a car from 30 km h–1 to 60 km h–1 if the mass of the car is 1500 kg?

Solution:
Mass of the car, m =1500 kg,

initial velocity of car, u = 30 km h–1= 30 × 1000m / 60 × 60s
= 25/3 m s–1
.
Similarly, the final velocity of the car,
v = 60 km h–1 = 50/3 m s–1
.
Therefore, the initial kinetic energy of the car,
K Ei = 1/2 m u2

= 1/2× 1500 kg × (25/3 m s–1)
= 156250/3 J.
The final kinetic energy of the car,
K E f = 1/2 × 1500 kg × (50/3 m s–1)
= 625000/3 J.
Thus, the work done = Change in kinetic energy
= KEi – KEf = 156250 J.

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