Question

As a simple pendulum of length ℓ sweeps back and forth in the arc of a circle, there are two forces acting on it: gravity m g and the force T exerted by the supporting string. As the pendulum swings, its speed and velocity continually change, meaning work is being done on it. Which force(s) do work?

Answer 1

Gravity

Step-by-step explanation:

Lets take the mass of the pendulum = m

Angle from vertical axis = θ

From the diagram

The gravity force mg have two component ,First one mg cosθ and other one is mg sinθ.

The component of gravity force mg sinθ is responsible for the motion of the pendulum ,that is why gravity does work in the pendulum.

Therefore the answer is -

Gravity