Work, Power and Efficiency

Question 1

How is work done?

Answer 1

Work is done when a force is applied and an object is moved a distance. This transfers energy.

Question 2

How would we define a joule?

Answer 2

1 Joule is the energy transferred when a force of 1 N causes a displacement of 1 m

Question 3

What is the value of the gravitational field
strength on the Earth and the Moon?

Answer 3

Earth: g = 9.8 N/kg
Moon: g = 1.6 N/kg

Question 4

What is power?

Answer 4

Power is the rate of transferring energy, also considered as the rate of doing work.

Question 5

How would we define a Watt?

Answer 5

1 Watt is equal to a transfer of 1 joule per second.

Question 6

What does it mean if a kettle has a 3 kW rating?

Answer 6

This kettle transfers 3000 J of energy to the thermal store of the water in it per second.
This kettle does 3000 J of work to the water in it every second.

Question 7

What is the law of conservation of energy?

Answer 7

Energy cannot be created or destroyed, only stored and transferred.

Question 8

What do we mean for a device to be efficient?

Answer 8

If a device is efficient it transfers its energy usefully.

Question 9

If a device is inefficient what does it do?

Answer 9

If a device is inefficient it loses energy to the surroundings (usually by heating), we call this energy dissipated or wasted, as it is transferred to less useful stores