How much work should be done on an object of $120 \, kg$ to increase its speed from $25 \, m s^{-1}$ to $40 \, m s^{-1}$ (in $, J$)?

$(a)$ Define power. Give its $SI$ unit.
$(b)$ Taking the example of a simple pendulum, explain the variations in the forms of energy and the interconversions involved.

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.

Explain that a flying bird possesses both potential and kinetic energy and provide their expressions.

Justify,giving proper reasoning,whether the work done in the following case is positive or negative: Work done by friction on a body sliding down an inclined plane.

$A$ force of $10\, N$ moves a body with a constant speed of $2\, m s^{-1}$. Calculate the power of the body.