Question

The diagram shows a swinging pendulum.

A pendulum hanging from a bar is shown in 3 positions. 1 is swung to the right, 1 to the left, and 1 in the middle. Solid lines connect the bob to he support in the right and left positions. A dotted line connects the bob to the support in the center position. Dotted lines connect right, left, and center along the arc of the pendulum swing.

Which best explains what happens to the motion of the pendulum due to the law of conservation of energy?

The pendulum will slow down and eventually stop moving as the mechanical energy transforms to thermal energy.
The pendulum will slow down and eventually stop moving as the mechanical energy disappears.
The pendulum will continue moving at the same speed because mechanical energy is created as the pendulum moves.
The pendulum will slow down but will not stop moving because some of the mechanical energy is destroyed.

Answer 1

"The pendulum will slow down and eventually stop moving as the mechanical energy transforms to thermal energy."

Explanation: friction and air resistance convert the pendulum’s mechanical energy (kinetic + potential) into thermal energy, so total energy is conserved but mechanical energy is dissipated as heat. (If no non‑conservative forces were present, it would keep swinging.)