(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) The energy stored in a body due to either its position or change in shape is known as potential energy. Water stored in a reservoir is an example of potential energy.
PE = mgh Where,
PE is the potential energy
m is the mass of the body
g is the acceleration due to gravity
h is the height above the surface of the earth
(b) Following are the differences between kinetic energy and potential energy:
(i) Kinetic energy is defined as the energy in body due to its motion while potential energy is defined as the energy due to its position.
(ii) Kinetic energy of a body when it is at rest is zero whereas the potential energy of a body when it is at rest is not zero.
(c) Mass of ball, m = 0.5 kg
Speed, v1 = 5 m/s
Speed, v2 = 3 m/s
KE1 = \(\frac{1}{2}\)m(v1)2
KE2 = \(\frac{1}{2}\)m(v2)2
Change in KE = KE1 – KE2 = 4J