Question

A child is swinging a swing. Minimum and maximum heights of swing from earths surface are 0.75 m and 2m respectively. The maximum velocity of this swing is:

• A. 5 m/s
• B. 10 m/s
• C. 15 m/s
• D. 20 m/s

Answer 1

Answer: (A)

5 m/s

Answer 2

Key Idea: Maximum kinetic energy of swing should be equal to difference in potential energies to conserve energy. From energy conservation $\frac{1}{2}mv_{\max }^{2}=mg({{H}_{2}}-{{H}_{1}})$ Here, ${{\text{H}}_{\text{1}}}\text{=}$ maximum height of swing from earths surface $=0.75\,m$ ${{H}_{2}}=$ maximum height of swing from earths surface $=2\,m$ $\therefore$ $\frac{1}{2}mv_{\max }^{2}=mg(2-0.75)$ or ${{v}_{\max }}=\sqrt{2\times 10\times 1.25}=\sqrt{25}=5\,m/s$