A) 5 m/s
B) 10 m/s
C) 15 m/s
D) 20 m/s
Correct Answer: A
Solution :
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, \[{{H}_{1}}=\] minimum height of swing from earth's surface = 0.75 m \[{{H}_{2}}=\] maximum height of swing from earth's surface = 2m \[\therefore \frac{1}{2}mv_{\max }^{2}=mg\,(2-0.75)\] \[or{{v}_{\max }}=\sqrt{2\times 10\times 1.25}\] \[=\sqrt{25}=5\,m/s\]
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