Question

Work done on a system puts energy into it. Work done by a system removes energy from it. Give an example for each statement.

Short answer

When a person pushes the lawn mower, it increases the energy system and the mower starts moving with constant velocity. Once the lawn mower starts moving due to friction, it starts losing energy in the form of heat, and finally it stops.

Step-by-step solution

Definition of the concept.

Work energy theorem: According to the work-energy theorem, the change in kinetic energy of the body equals the work done on the body.

In other words, when the kinetic energy of the body increases, the work is done on the system and when the kinetic energy of the system decreases, the work is done by the system.

Work on a system that adds energy to it.

When the work is done on the system, the final kinetic energy of the system will be greater than the initial kinetic energy of the system before the application of force on the system.

Assuming a lawn mower is initially at rest. A gardener pushes the lawn mower (work is done on the mower), so the gardener increases the energy of the mower and it starts to move.

Therefore, work performed on a system adds energy to it.

A system's work depletes its energy.

When the work is done by the system, the final kinetic energy of the system will be smaller than the initial kinetic energy of the system before the application of force on the system.

Assuming a lawn mower is moving. There is a frictional force acting between the lawn mower and the lawn. To overcome this friction, the mower has to do work against it (work is done by the system), so the friction decreases the energy of the mower and finally it stops.

Therefore, the work done by a system removes energy from it.