Which would have a greater effect on the kinetic energy of an object - doubling the mass,or doubling the velocity?

State whether the following statement is true or false:
When energy changes from one form to another,the energy that disappears from one form reappears in an exactly equivalent amount in the other form.

Given below are a few situations. Study them and state in which of the given cases work is said to be done. Give a reason for your answer:
$(i)$ $A$ person pushing hard a huge rock,but the rock does not move.
$(ii)$ $A$ bullock pulling a cart up to $1 \, km$ on the road.
$(iii)$ $A$ girl pulling a trolley for about $2 \, m$ distance.
$(iv)$ $A$ person standing with a heavy bag on his head.

$A$ light body and a heavy body have the same kinetic energy. Which one will have the greater momentum?

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 $(-ve)$,positive $(+ve)$,or zero $(0)$.

Name the practical unit of power in engineering.