State the energy conversions in a dry cell.

The potential energy of a person is minimum when:

Identify the energy possessed by a rolling stone.

$A$ porter moving vertically upstairs with a load on his head does work. Why?

$A$ crane pulls up a car weighing $500 \, kg$ to a vertical height of $4 \, m$. Calculate the work done by the crane. (in $J$)

An electric motor of power $100\, W$ is used to drive the stirrer in a water bath. If $50\%$ of the energy supplied to the motor is spent in stirring the water, calculate the work done on the water in one minute. (in $J$)