Question

Write two conditions where zero work is done even though force is applied.

When does the work done is negative? Write one example.

Derive relation between S.I and CGS units of work.

Name the physical quantity measured in kilowatt hour? How is kilowatt hour related with SI unit of that physical quantity?

A weight lifter lifts a load of 200 kgf to a height of 2.5m in 5 seconds. Calculate
i) the work done by him
ii) power developed by him (g=10m/s2)


correct answer only otherwise it will be reported ​

Answer 1

(i) If the displacement of the body is in the direction of force. then work done is positive.
Hence, F×S
For example: A coolie does work on the load when he raises it up against the force of pavity. The force exerted by coolie (=mg) and displacement. both an in upward direction.
(ii) If the displacement of the body is in the direction opposite to the force. then work done is negative.
Hence, W=−F×S
For example: When a body moves on a surface. the force of friction between the body and the surface is in direction opposite to the motion of the body and so the work done by the force of friction is negative.