Question

a child swings on a swing at the playground. the motion of the swing resembles the motion of a pendulum. when is kinetic energy of the swing zero? when it is moving the fastest it is never zero. when it stops moving at the top of the swing at the bottom of the swing

Explanation:

Kinetic energy \(K = \frac{1}{2}mv^{2}\), where \(m\) is mass and \(v\) is velocity. When the swing stops moving (at the top of its arc), \(v = 0\). Substituting \(v = 0\) into the kinetic - energy formula gives \(K=\frac{1}{2}m\times0^{2}=0\).
When moving the fastest (at the bottom of the swing), \(v\) is maximum, so \(K\) is maximum. And it is not correct to say it is never zero as there are points (at the top of the swing) where \(v = 0\).

Answer:

when it stops moving at the top of the swing