Two students analyze the swing of a long frictionless pendulum bob of mass released…
PHYSICS · Multi-part · A Level · Physics · Mechanics and materials · Mechanics and materials
Problem
Two students analyze the swing of a 1.2m long frictionless pendulum bob of mass 0.40kg released from rest at an angle of 15∘ from the vertical. Student 1 chooses the zero of gravitational potential energy at the lowest point of the swing, while Student 2 chooses it at the release point.
(a) Explain whether the numerical values of the gravitational potential energies calculated by the two students at an arbitrary point during the swing will be the same or different. Support your answer qualitatively without calculation.
(b) Both students calculate the speed of the bob as it passes through the lowest point. Show algebraically that, despite their different reference levels, they must obtain identical values for this speed.
(c) Generalize your reasoning to explain why the physical predictions for any isolated mechanical system are independent of the chosen zero level for potential energy.