NCERT Class 9 Science Solutions: Chapter 11 – Work and Energy Part 1

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Question 1:

Q. A force of acts on an object. The displacement is, say , in the direction of the force (Figure). Let us take it that the force acts on the object through the displacement. what is the work done in this case?

Q 1 Image-Showing Forece Of Objects.

Q 1 Image-Showing Forece of Objects.

Q 1 Image-Showing Forece Of Objects.

Answer:

When force acts on an object to displace it through a distance in its direction, then the work done on the body by the force is given by:

Work done Force Displacement

Where,

N

m

Therefore, work done,

Question 1:

Q. When do we say that work is done?

Answer:

Work is done whenever the given conditions are satisfied:

  • A force acts on the body.

  • There is a displacement of the body caused by the applied force along the direction of the applied force.

Question 2:

Q. Write an expression for the work done when a force is acting on an object in the direction of its displacement.

Q 2 Image Showing Work And Kinetic Energy.

Q 2 Image Showing Work and Kinetic Energy.

Q 2 Image Showing Work And Kinetic Energy.

Answer:

When a force diaplaces a body through a distance in the direction of the applied force, then the work doen on the body is given by the expression:

Work done Force Displacement

Question 3:

Q. Define 1 j of work

Answer:

1 J is the amount of work done by a force of on an object that displaces it through a distance of 1 in the direction of the applied force.

Question 4:

Q. A pair of bullocks exerts a force of on a plough. The field being ploughed is long. How much work is done in ploughing the length of the field?

Answer:

Work done by the bullocks is given by the expression:

work done force displacement

Applied force,

Displacement,

Hence, 2100 of work is done in ploughing the length of the field.