Question

Which one among the following happens when a swing rises to a certain height from its rest position?
A). Its potential energy decreases while kinetic energy increases
B).Its kinetic energy decreases while potential energy increases
C).Both potential and kinetic energy decrease
D). Both potential and kinetic energy increase

Answer 1

When a swing is in the rest position there is no potential energy acting on it, it only possesses kinetic energy. As it is raised to a certain height its potential energy is increased and the kinetic energy is decreased.

Complete Step By Step Answer:
Potential energy is given by $PE = mgh$
Where m is the mass, g is the acceleration due to gravity and h is the height to which it is raised.
The total energy of the system is given by $TE = PE + KE$ . Potential energy is the stored energy and kinetic energy is the energy in motion. Together these two constitute the mechanical energy of the swing.
But the total energy is conserved, therefore as the potential energy increases the kinetic energy decreases and vice versa.
Option B (Its kinetic energy decreases while potential energy increases) is the correct answer.

Note:
The entire mechanical energy of the swing is potential energy, at its beginning. It doesn't have kinetic energy, as it doesn't move. As the swing descends, part of its potential energy is transformed into kinetic energy. At its lowest point, the kinetic power of the swing is at its best because it moves quickly. Its potential energy is at minimum since the swing is at its lowest point. The swing gathers potential energy again as it rises. Once again, at the peak of its arc, it possesses zero kinetic energy and maximum potential energy.