Work

Name the type of energy (kinetic or potential) possessed by the following:

(g) A stretched rubber band.

In which of the following cases is work being done:

_____ is said to be done by a force on the body when the body displaces.

A coolie does no work against the force of gravity while carrying a luggage on a road.

It takes $20 \mathrm{s}$ for a girl A to climb up the stairs while girl B takes $15 \mathrm{s}$ for the same job. Compare the work done by both the girls.

A truck of mass $1000 \mathrm{kg}$, increases its speed from  $36 \mathrm{km} {\mathrm{h}}^{-1} \mathrm{to} 72 \mathrm{km} {\mathrm{h}}^{-1}$ . Find the increase in its kinetic energy.

A pump raises water by spending  $4\times {10}^5 \mathrm{J}$ of energy in $10 \mathrm{s}$. Find the power of pump.

State the energy changes in a microphone while in use.

State the energy changes in an electric motor while in use.

State the energy changes in a loud speaker while in use.

Give reasons for the following:

(d) A teacher moving around in the class is doing work but a child standing and reading a book is not doing any work.

Give reasons for the following:

(a) No work is done if a man is pushing against a wall.

State two factors on which the work done on a body depends.

A body of mass $\mathrm{m}$ is moved from ground to a height $\mathrm{h}$. If force of gravity on mass of $1 \mathrm{kg} \mathrm{is} \mathrm{g}$ newton, find the work done in lifting the body.

Write the expression for work done by a force.

The moon is revolving around the earth in a circular path. How much work is done by the moon?

A coolie is moving on a road with a luggage on his head. Does he perform work against the force of gravity? Give reason for your answer.