Calculate the power of an electric motor that can lift $800 \, kg$ of water to store in a tank at a height of $1500 \, cm$ in $20 \, s$. $(g = 10 \, m s^{-2})$ (in $, kW$)

$(a)$ Define work. State two factors on which the magnitude of work depends.
$(b)$ $A$ car and a truck have the same speed of $30 \, m/s$. If their masses are in the ratio $1:3$,find the ratio of their kinetic energy.

Why is the water at the bottom of a waterfall warmer than the water at the top?

$(a)$ Define one watt.
$(b)$ $A$ lamp consumes $1000 \ J$ of electrical energy in $10 \ s$. What is its power?

List two conditions which need to be satisfied for the work to be done on an object.

Justify giving proper reasoning whether the work done in the following case is positive or negative: Work done by a man in lifting a bucket out of a well by means of a rope tied to the bucket.