The diagram shows a swinging pendulum.

which best explains what happens to the motion of the pendulum?

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

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

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

d. the pendulum will slow down but will never stop moving because energy cannot be destroyed.

The correct answer is

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

In fact, we must keep in mind the presence of the air, which causes some resistance to the motion of the pendulum. As the pendulum moves through the air, part of its mechanical energy is transferred to the molecules of air because of the friction of this molecules with the surface of the pendulum. As a result, the pendulum slows down, and eventually stops. The initial energy of the pendulum has been converted into thermal energy of the molecules of air, which move faster now.

the working equation for the angular size is the product of the physical size and 360 degrees divided by the product of two pi and distance from earth. the minimum size would be 0.559 degrees while the maximum size would be 0.49 degrees.