Question

Numerical based questions of physics
on work and energy of class 9

Answer 1

Question 1 -  A force of 10 N acts on an object. The displacement is 8 min the direction of the force. What is the work done in this case?

Given :

Force = 10 N ; Displacement = 8 m

To Find :

Work Done

Solution:

We know,

Work done (W) = Force (F) × Displacement (S)

⇒                  W = F × S

⇒                  W = 10 × 8

⇒                  W = 80 Nm

∴                   W = 80 J

Therefore, Work done by the force is 80 J

Question 2 - A pair of bullocks exerts a force of 100 N on a plough. The field being ploughed is 15 m long. How much work is done in ploughing the length of the field?

Given :

Force (F) = 100 N

Displacement (S) = 15 m

To Find :

Work done in ploughing the length of the field

Solution:

We know,

Work done (W) = Force (F) × Displacement (S)

⇒                  W  = F × S

⇒                  W  = 100 × 15

∴                   W  = 1500 J

Therefore, 1500 J of work is done in ploughing the length of the field.

Answer 2

Answer:

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

Explanation:

V=30 Km * 60 Km = 1800 km
m=1500 kg

we know that  K.E. = 1/2 m v2
KE= 1/2 * 1500 * 1800
=1800*750
=126000