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Question
The figure below shows a simple pendulum of mass 200 g. It is displaced from the mean position A to the extreme position B. The potential energy at the position A is zero. At the position B the pendulum bob is raised by 5 m.
- What is the potential energy of the pendulum at the position B?
- What is the total mechanical energy at point C?
- What is the speed of the bob at the position A when released from position B?
(Take g = 10 ms-2, given that there is no loss of energy.)
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Solution
- U = mgh = 0.2 × 10 × 5
U = 10 J - According to the rule of conservation of mechanical energy, mechanical energy is constant wherever the pendulum's bob rotates.
∴ Mechanical energy at point C = 10 J - By principle of conservation of energy
U at the top = K at the bottom
∴ `10 = 1/2 xx 0.2 xx v^2`
∴ v2 = 100
∴ v = 10 m s-1
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