State carefully if the following quantities are positive or negative:�

1.	State carefully if the following quantities are positive or negative: 1. work done by a man in lifting a bucket out of a well by means of a rope tied to the bucket. 2. work done by gravitational force ‘in the above case, 3. work done by friction on a body sliding down an Inclined plane, 4. work done by an applied force on a body moving on a rough horizontal plane with uniform velocity, 5. work done by the resistive force of air on a vibrating pendulum in bringing it to rest.
Answer» 1. We know that: W = \(\vec F,\vec S\) FS cosθ ‘Positive’ Reason: Force is acting in the direction of displacement (θ = 0°) 2. ’Negative’ Reason: Force is acting in the opposite direction to displacement (θ = 180°) 3. ’Negative’ Reason: Force of friction is opposite to the displacement (θ = 180°) 4. ‘Positive’ Reason: The body mover in the direction of force applied (θ = 0°) 5. ‘Negative’ Reason: The resistive force opposes the motion (θ = 0°)

State carefully if the following quantities are positive or negative: 1. work done by a man in lifting a bucket out of a well by means of a rope tied to the bucket. 2. work done by gravitational force ‘in the above case, 3. work done by friction on a body sliding down an Inclined plane, 4. work done by an applied force on a body moving on a rough horizontal plane with uniform velocity, 5. work done by the resistive force of air on a vibrating pendulum in bringing it to rest.

Answer»

1. We know that: W = \(\vec F,\vec S\) FS cosθ

‘Positive’

Reason: Force is acting in the direction of displacement (θ = 0°)

2. ’Negative’

Reason: Force is acting in the opposite direction to displacement (θ = 180°)

3. ’Negative’ Reason: Force of friction is opposite to the displacement (θ = 180°)

4. ‘Positive’ Reason: The body mover in the direction of force applied (θ = 0°)

5. ‘Negative’ Reason: The resistive force opposes the motion (θ = 0°)