Define work. Give its SI and CGS units. What is the relationship between these units?

Give an example for

(a) force acting in the direction of displacement.

(b) force acting against the direction of displacement.

(c) force acting perpendicular to the direction of displacement.

Define potential energy. On what factors does potential energy depend.

Two persons of the same weight climb a rope to a height of $\mathit{8}\mathit{ }\mathrm{m}$. The first person takes $\mathit{10} \mathrm{s}$ while the second takes $\mathit{20} \mathrm{s}$ to complete the task. What is the work done by the two persons? Who did more work per unit time? (Take $g=m{s}^{\mathit{-}\mathit{2}}$)

A mass of $10 \mathrm{kg}$ is dropped from a height of $50 \mathrm{cm}$. Find its

(a) Potential energy just before dropping.

(b) kinetic energy just on touching the ground

(c) velocity with which it hits the ground.

$\left[g\mathit{=}\mathit{10} \mathrm{m}/{\mathrm{s}}^2\right]$

(a) A ball of mass $0.5 \mathrm{kg}$slows down from a speed of $5 \mathrm{m}/\mathrm{s}$ to $3 \mathrm{m}/\mathrm{s}$, calculate the change in the kinetic energy of the ball.

(b) Which would have a greater effect on the kinetic energy of an object-doubling the mass or doubling the velocity.

Name the energy transformation taking place in the following devices:

(a)

(i) a motor

(ii) a car engine

(iii) a radio

(iv) a nuclear reactor

(b) How much work is done, when earth moves around the sun in its orbit.