Someone's idea is for an electric fan that costs nothing to run. The electric motor which turns the fan also turns a generator. This produces electricity for the motor, so no battery or mains supply is needed! Explain why this idea will not work.

Which of the following is a true statement about the acceleration ~a of the pendulum bob ~a is equal to the acceleration due to gravity. ~a is perpendicular to the bob’s trajectory. ~a is equal to the instantaneous rate of change in velocity. ~a is tangent to the bob’s trajectory.