At the extreme displacement of a pendulum, which statement is true?

• A. Restoring force is zero
• B. Restoring force is at a maximum
• C. Kinetic energy is maximum
• D. Speed is maximum

Answer: (B)

The main idea is that the restoring force on a pendulum grows with how far it is displaced from equilibrium. At the furthest point, the pendulum’s velocity is momentarily zero, but the gravity component pulling it back along the arc is largest in magnitude because it’s proportional to sin of the angle. That tangential restoring force points toward the vertical and is strongest when the angle is largest, so the restoring force is at a maximum here. The speed (and thus kinetic energy) is zero at this instant since the pendulum just pauses before reversing direction. So the correct statement is that the restoring force is at a maximum.