A small pendulum bob of mass m is suspended from a light string of length L. The bob is released from rest when the string makes an initial angle of 30° with the vertical. Air resistance is negligible.
Address the questions below regarding the interchange of gravitational potential energy U and kinetic energy K during one complete swing.
(a) Describe qualitatively how U and K change as the bob moves from its release point to the lowest point in its arc. Your answer should explain which form of energy increases, which decreases, and why.
(b) Explain why the bob’s speed is zero both at the initial release point and at the symmetric point on the opposite side, using only energy considerations (no explicit references to forces are required).
(c) Identify the point along the bob’s trajectory where the tension in the string is greatest. Justify your answer by relating tension to the distribution of U and K and to the bob’s speed.