What is a watt?

$(a)$ What is meant by potential energy? Is potential energy a vector or scalar quantity?
$(b)$ Give one example of a body having potential energy.

An iron sphere of mass $10 \, kg$ has the same diameter as an aluminium sphere of mass $3.5 \, kg$. Both spheres are dropped simultaneously from a tower. When they are $10 \, m$ above the ground,they have the same

What happens to the kinetic energy when
$(i)$ the mass of the body is doubled at constant velocity?
$(ii)$ the velocity of the body is doubled at constant mass?
$(iii)$ the mass of the body is doubled but the velocity is reduced to half?

$A$ man rowing a boat upstream is at rest with respect to the shore. Is he doing work?

One joule of work is said to be done when: