When do we say that work is done?

What are the various energy transformations that occur when you are riding a bicycle?

What is the work done by the force of gravity on a satellite moving around the Earth? Justify your answer.

In each of the following cases,a force,$F$ is acting on an object of mass,$m$. The direction of displacement is from west to east,shown by the longer arrow. Observe the diagrams carefully and state whether the work done by the force is negative,positive,or zero.

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.

What is power?