Question

Example 11.4 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?​

Answer 1

Explanation:

Initial velocity u=30 km/h=30×

18

5

=

3

25

m/s

Final velocity v=60 km/h=60×

18

5

=

3

50

m/s

Mass m=1500 kg

Work done W=

2

1

mv

2

−

2

1

mu

2

⟹ W=

2

m

(v

2

−u

2

)=

2

1500

×((

3

50

)

2

−(

3

25

)

2

)=156187 J

Answer 2

Answer:

Work done is 156250 J.

Explanation:

Given,

The mass (m) of the car is 1500 kg.

Initial velocity of car = u = 30 km / hr = 30 * 5/18 = 25 / 3 m/s

Final velocity of car = v = 60 km / hr = 60 * 5/18 = 50/3 m/s

To find: The work to be done to increase the velocity of a car from

30 km h-1 to 60 km h^-1

Solution:

Initial kinetic energy = Ki = 1/2mu² = 1/2*1500*25/3 * 25/3 = 156250/3 J

Final Kinetic energy = Kf = 1/2mv² = 1/2*1500*50/3*50/3 = 625000/3 J

Work done can be given as change in Kinetic Energy,

i.e W = ΔK.E

or, W = Kf -  Ki

or, W = 625000/3 - 156250/3

or, W = 156250 J

Therefore, Work done is 156250 J.