Question

17. Calculate the work required to be done to stop a car of 1500 kg
moving at a velocity of 60 km/h?
​

Answer 1

When a object is moving with a constant velocity, it possess K.E
K.E=
2
1
​
×m×v
2


So, in order to bring the object to rest i.e its same magnitude of energy is required so, as the final final energy comes to zero.

v=60km/hr=16.66m/s
So, magnitude of work that needs to be done =
2
1
​
×m×v
2

Hence, work required to stop the car =
2
1
​
×1500×16.66
2
=208166.7J= 208.17kJ

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.