Question

2. Give examples of zero work, positive work
and negative work.​

Answer 1

Positive Work

If a force displaces the object in its direction, then the work done is positive

So, W=Fd

The example of this kind of work done is motion of ball falling towards ground where displacement of ball is in the direction of force of gravity.

Positive work done

Negative work

If the force and the displacement are in opposite directions, then the work is said to be negative. For example if a ball is thrown in upwards direction, its displacement would be in upwards direction but the force due to earth’s gravity is in the downward direction.

negative work done

So here in this case gravity is doing negative work when you throw the ball upwards. Hence the work done by gravitational force is negative. Mathematically when displacement is opposite to the force work done is given by

Negative work just means that the force and the displacement act in opposite directions.

Case of zero work done

If the directions of force and the displacement are perpendicular to each other, the work done by the force on the object is zero.

case of zero work done

For example, when we push hard against a wall, the force we are exerting on the wall does no work, because in this case the displacement of the wall is d = 0. However, in this process, our muscles are using our internal energy and as a result we get tired.

Answer 2

Answer:

Example of zero work: applying a force to roll a 1kg ball to 1m then applying the same force over the same distance in the opposite direction returning ball to normal.

Positive work: pushing a object in forward direction.

Negative work: If the ball is thrown upwards but the force exerted by the gravity on it is negative force.