Final answer:
The ratio of output work to input work represents the efficiency of a motor. An object not in motion has gravitational potential energy due to its distance from Earth. This energy contributes to the object's mechanical energy, which remains constant in a closed system according to the Law of Conservation of Mechanical Energy. Option C is correct.
Step-by-step explanation:
The efficiency of a motor can be expressed as the ratio of output work to input work, and it's typically presented as a percentage. When an object is not in motion but has energy because of its position relative to Earth, it possesses gravitational potential energy (C).
This form of energy is part of what we call mechanical energy, which also includes kinetic energy—the energy due to an object's motion. The Law of Conservation of Mechanical Energy states that in a closed system without external dissipative forces, such as friction or air resistance, the total mechanical energy remains constant.
Gravitational potential energy is calculated based on an object's mass, the acceleration due to gravity, and its height above a reference point. An object at rest on Earth's surface still has gravitational potential energy because it has the potential to fall or move due to gravity's pull.