Question

2. A 14.8-kg child sits in a 1.30-kg swing. You pull the swing back, lifting it 52.1 cm vertically, and then let go. Determine the speed of the child and swing as the swing moves past its lowest point.

Answer 1

To answer this problem, we have to define the two energies, Potential and Kinetic Energy.

Initially when the child is at rest at 52.1 cm, the potential energy PE is at its highest.

PE = m g h

Where,

m = total mass = 14.8 kg + 1.30 kg = 16.10 kg

g = gravitational acceleration = 9.8 m /s^2

 h = height = 52.1 cm = 0.521 m

Computing for PE:

PE = 16.10 * 9.8 * 0.521

PE = 82.29 N

As the swing moves past its lowest point h = 0, then all PE is converted to Kinetic Energy KE. Therefore, at lowest point

KE = 82.29

KE = 0.5 m v^2

0.5 (16.10) v^2 = 82.29

v = 3.20 m/s