Summary: There are two questions about the motion of simple pendulum. The first one is about the conservation of energy in a pendulum and the second one talks about the frequency and the period of a certain length of pendulum.

https://blogs.ubc.ca/phys101/files/gravity_forms/1-72f8f8fec225ededbd95c074100f3d9f/2015/02/IMG_3856-copy.jpeg