Final answer:
The question involves energy transformation where mechanical energy is often converted to internal energy or heat within an engine, and an electric motor changes electrical energy to mechanical energy. Conservation of energy ensures the total mechanical energy in a closed system remains constant. A heat engine converts thermal energy into mechanical energy.
Step-by-step explanation:
The question pertains to the transformation of energy during a process, which can occur in various forms such as mechanical, kinetic, potential, and heat energy. Within an engine, unused mechanical energy is often converted into internal energy and heat, as described in question 37.
An electric motor predominantly converts electrical energy into mechanical energy, facilitating various applications such as turning wheels or moving parts of machines, elucidated in question 7.
The concept of conservation of energy is seen in the fact that the sum of kinetic and potential energies in a closed system remains constant, with transformations from one form to another taking place without any loss of the total mechanical energy.
When we talk about energy transfer to the human body, we are referring to processes such as absorbing sunlight (heat transfer), ingesting food (internal energy due to metabolism), and riding an elevator which involves doing work against gravity as explained in question 7.
A heat engine is a device that primarily converts thermal energy into mechanical energy, which can then be used to perform work as stated in question 19 of the Check Your Understanding section.