A simple pendulum of length swings back and forth with small amplitude in a room…
PHYSICS · Multi-part · CBSE · Physics · Work, Energy and Power · Work, Energy and Power
Problem
A simple pendulum of length L swings back and forth with small amplitude in a room where air resistance is negligible. Two students discuss how to analyze the pendulum’s mechanical energy.
• Student A chooses the lowest point of the swing as the location where the pendulum’s gravitational potential energy is defined to be zero.
• Student B instead chooses the height of the pendulum bob at the left–hand turning point as the location where gravitational potential energy is zero.
Answer the following questions about the consequences of each choice.
(1) Describe qualitatively how the numerical values of the pendulum’s gravitational potential energy, kinetic energy, and total mechanical energy at the lowest point of the swing differ for the two students. You may use words or symbolic expressions, but do not perform numerical calculations.
(2) Explain why both students must nevertheless agree on the speed of the pendulum bob at the lowest point, even though their individual numerical values of gravitational potential energy differ.
(3) Student B claims that, because the total mechanical energy calculated with their reference choice is zero at the left–hand turning point, no work is required to set the pendulum into motion from rest at that position. Evaluate the validity of this claim and justify your reasoning.