(a) Explain by an example what is meant by potential energy. Write down the expression for gravitational potential energy of a body of mass m placed at a height h above the surface of the earth.
(b) What is the difference between potential energy and kinetic energy?
(c) A ball of mass $0.5\ kg$ slows down from a speed of $5\ m/s$ to that of $3\ m/s$. Calculate the change in kinetic energy of the ball. State your answer giving proper units.

(a). Potential Energy: The energy of a body due to its position is known as the gravitational potential energy of the body.

If a body of mass $m$ is placed at a height $h$ above the surface of the earth, then its potential energy $P=mgh$

Here, $g\rightarrow$gravitational acceleration

(b). Difference between potential energy and kinetic energy:

Potential Energy	Kinetic Energy
1. A body possesses potential energy due its virtue of positions.	1. A body possesses kinetic energy due to its motion.
2. It depends on the height of the body from the surface of the ground.	2. It depends on the velocity of the of the moving body.
3. A stone placed on the roof is a good example of possessing potential energy.	3. A car moving on the road is a good example of bdy possessing kinetic energy.

(c). Mass $m=0.5\ kg$

Initial speed $v_1=5\ m/s$

Final speed $v_2=3\ m/s$

Change in kinetic energy $=K_1-K_2$

$=\frac{1}{2}mv_1^2-\frac{1}{2}mv_2^2$

$=\frac{1}{2}m(v_1^2-v_2^2)$

$=\frac{1}{2}\times0.5\times(5^2-3^2)$

$=\frac{1}{2}\times0.5\times(25-9)$

$=\frac{1}{2}\times0.5\times16$

$=4.0\ J$

Thus, there is a change in kinetic energy of $4.0\ J$

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Updated on: 10-Oct-2022

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