Question 6
Work, Energy and PowerA simple pendulum of mass m moves along an arc of a circle radius R in a vertical plane as shown in the figure above. What is the work done by gravity in a downward swing through the angle θ to 0°?
- A.mgR sin θ
- B.mgR (1 − cos θ)
- C.mgR
- D.mgR (1 − sin θ)
Show the answer and explanation
Answer: B (mgR (1 − cos θ))
Explanation
At angle θ the bob is R(1 − cos θ) higher than at the bottom, so gravity does work mgR(1 − cos θ) as it swings down.