Answer
At the bottom. At the endpoints. Half its value.
Work Step by Step
a. KE + PE = constant. The KE is maximum where the pendulum moves fastest. At the lowest point, KE is maximum and PE is minimum.
b. PE is maximum at the endpoints where the bob momentarily stops and KE is zero.
c. Total energy = KE + PE = constant. When KE is half its maximum value, then PE is also half its maximum value. The bob is exactly halfway in height between its lowest and highest points.
