Question

At what point does the bob have nonzero radial acceleration and zero tangential acceleration?

Answer 1

In circular motion, the bob has nonzero radial acceleration and zero tangential acceleration when the net force on the bob is tangent to the arc and equals -mg sin 0.

Step-by-step explanation:

In circular motion, the bob has nonzero radial acceleration and zero tangential acceleration at the point where the net force on the bob is tangent to the arc and equals -mg sin 0. This happens when the weight mg has components mg cos 0 along the string and mg sin tangent to the arc, and the tension in the string exactly cancels the component mg cos parallel to the string. At this point, there is a net restoring force back toward the equilibrium position.