$A$ pair of bullocks exerts a force of $140 \, N$ on a plough. The field being ploughed is $15 \, m$ long. How much work is done in ploughing the length of the field (in $, J$)?

$A$ person holds a bundle of hay over his head for $30$ minutes and gets tired. Has he done some work or not? Justify your answer.

Illustrate the law of conservation of energy by discussing the energy changes which occur when we draw a pendulum bob to one side and allow it to oscillate. Why does the bob eventually come to rest? What happens to its energy eventually? Is it a violation of the law of conservation of energy?

Look at the activities listed below. Reason out whether or not work is done in the light of your understanding of the term 'work'.
$1$. Suma is swimming in a pond.
$2$. $A$ donkey is carrying a load on its back.
$3$. $A$ windmill is lifting water from a well.
$4$. $A$ green plant is carrying out photosynthesis.
$5$. An engine is pulling a train.
$6$. Food grains are getting dried in the sun.
$7$. $A$ sailboat is moving due to wind energy.

Soni says that the acceleration in an object could be zero even when several forces are acting on it. Do you agree with her? Why?

The kinetic energy of an object of mass,$m$ moving with a velocity of $5 \,m \,s^{-1}$ is $25\, J$. What will be its kinetic energy when its velocity is doubled? What will be its kinetic energy when its velocity is increased three times?