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.

The mechanical energy transforms to thermal energy as the pendulum slows and eventually stops moving.

Explanation:

1. The mechanical energy transforms to thermal energy as the pendulum slows and eventually stops moving.

This statement is true: the mechanical energy is the kinetic and potential energy.

When the pendulum swings, it exchanges potential and kinetic energy: when the pendulum is at the highest altitude, the potential energy is maximum, and the kinetic energy is zero; when the pendulum is at the lowest altitude, the potential energy is zero and the kinetic energy is maximum.

Nevertheless, due to the friction with air, part of the energy is transformed into thermal energy (heat) all the time the pendulum is moving. At the end, all the mechanical energy is transformed into thermal energy, and the pendulum stops.

2. The mechanical energy disappears as the pendulum slows and eventually stops moving.

This is false. As per the law of conservation of energy the enery does not dissapear but transformed into other forms: mechanical energy can be transformed into thermal or sound energy, or other forms of energy.

3. The pendulum will continue moving at the same speed until someone stops it because energy cannot be destroyed.

This is false. The friction with air causes the conversion of mechanical energy into thermal energy, and the pendulum will stop enven in no one stops it.

4. The pendulum will slow down but will never stop moving because energy cannot be destroyed.

This is false. As explained above the pendulum will slow down and stop moving because the mechanical energy will transform in thermal energy.

Explanation:

the duration of a photographic flash is related to an rc time constant, which is 0.100 μs for a certain camera.