Check sibling questions

In each of the following a force, F is acting on an object of mass, m. The direction of displacement is from west to east shown by the longer arrow. Observe the diagrams carefully and state whether the work done by the force is negative, positive or zero

NCERT Image Q 18.png

Answer

We know that

Work done = Force × Displacement × cos θ

Where, theta is the angle between the force and the displacement

 

Case1

f1.png

The angle between the force and displacement is 90 degrees.

Work done = Force × Displacement × cos θ

        = Force × Displacement × cos 90

        = Force × Displacement × 0

        = 0

 

Hence, work done is 0 .

 

Case 2

f2.png

 

The angle between the force and displacement is 0 degrees.

    Work done = Force × Displacement × cos θ

= Force × Displacement × cos 0

= Force × Displacement × 1

= Force × Displacement

 

Hence, work done is positive .

 

Case 3

f3.png

 

The angle between the force and displacement is 180 degrees.

    Work done = Force × Displacement × cos θ

= Force × Displacement × cos 18 0

= Force × Displacement × (-1)

= - Force × Displacement

Hence, the work done is negative.

 

Introducing your new favourite teacher - Teachoo Black, at only ₹83 per month

CA Maninder Singh's photo - Expert in Practical Accounts, Taxation and Efiling

Made by

CA Maninder Singh

CA Maninder Singh is a Chartered Accountant for the past 12 years and a teacher from the past 16 years. He teaches Science, Accounts and English at Teachoo