Select the statement that accurately summarizes mechanical energy.

D) Mechanical energy is the sum of kinetic and potential energy.

Select the statement(s) that are true about the energy an object contains as it moves along a frictional surface.

A) The presence of friction visibly changes the speed or motion of the object.
B) Final thermal energy is equal to the initial mechanical energy of the object.
C) Friction is the energy created when an object encounters a surface.
D) The object's energy is destroyed due to the presence of friction.
E) Mechanical energy of the object decreases as temperature of the surface increases.

The true statement(s) about the energy an object contains as it moves along a frictional surface are:

A) The presence of friction visibly changes the speed or motion of the object.
E) Mechanical energy of the object decreases as the temperature of the surface increases.

Statement B is incorrect because final thermal energy is typically less than the initial mechanical energy due to energy loss to friction, and statement C is misleading because friction is not "energy created" but a force that opposes motion, and statement D is not completely accurate since energy is not destroyed but transformed (usually into thermal energy).

Therefore, A and E are the suitable choices.

Select the statement that accurately summarizes the conversion of energy in a pendulum system.

A) A pendulum cannot have gravitational potential energy and kinetic energy at the same time.
B) Kinetic energy is inversely proportional to the gravitational potential energy of the object.
C) Gravitational potential energy and kinetic energy are at their maximum at the highest position.
D) Mechanical energy changes as kinetic energy is converted.

The statement that accurately summarizes the conversion of energy in a pendulum system is:

A) A pendulum cannot have gravitational potential energy and kinetic energy at the same time.

However, please note that this statement is actually misleading; a pendulum does have both types of energy at different points during its swing.

The more suitable statement for a pendulum's energy conversion is:

**B)** Kinetic energy is inversely proportional to the gravitational potential energy of the object.

This effectively means that when potential energy is high (at the highest points of the swing), kinetic energy is low, and vice versa, thus demonstrating energy conservation in the system.

Thus, the best option that captures the fundamental behavior of energy conversion in a pendulum is **B)**.

(Note: If "accurately summarizes" is interpreted strictly, none of the provided statements are perfectly accurate for a pendulum; however, **B)** is the closest in terms of energy relationship.)