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. ○ at the bottom of the swing ○ when it stops moving at the top of the swing

Explanation:

Kinetic energy ($KE$) is given by the formula $KE = \frac{1}{2}mv^2$, where $m$ is mass and $v$ is velocity. When velocity $v = 0$, $KE = 0$. A swing (pendulum - like motion) stops momentarily at the top of its swing (turning point) before moving back down. At this point, its velocity is zero, so kinetic energy is zero. Let's analyze the options:

• "when it is moving the fastest": At the bottom of the swing, velocity is maximum, so $KE$ is maximum (not zero). Eliminate this.
• "It is never zero": This is incorrect because at the top of the swing, velocity is zero, so $KE$ is zero. Eliminate this.
• "at the bottom of the swing": At the bottom, velocity is maximum, so $KE$ is maximum. Eliminate this.
• "when it stops moving at the top of the swing": At the top, the swing stops momentarily (velocity = 0), so $KE = \frac{1}{2}m(0)^2 = 0$. This is correct.

Answer:

when it stops moving at the top of the swing