Energy is a key principle in physics, as it allows work to be done. The rate at which energy is transferred is called power and the amount of energy that is usefully transferred is called efficiency.
Which is a correct example of work being done?
An apple sitting still on a table
A shelf holding up a book
A toy car being pushed across the floor
What are the correct units for work?
Work is measured in joules (J)
Work is measured in amps (A)
Work is measured in newtons (N)
How much work is done by a 10 N force pushing a box 4 m across the floor?
If a motor does 500 J of work to lift a 200 N weight, how high was the weight lifted?
Which of the following is a definition of power?
The amount of work done by a certain force
The energy transferred × time taken
The amount of work done ÷ time taken
A hair dryer transforms 10,000 J of energy in 4 s. What is its power?
A 60 W lamp is left on for 20 s. How much energy has been transformed?
In an electric kettle, what energy is not wasted?
The energy that heats the water
The energy that dissipates out of the kettle into the surroundings
The sound heard as the kettle boils
What is the percentage efficiency of Christmas lights that give out 10 W of light radiation for an electrical power input of 200 W?
How might a toy car be made more efficient?
Push it with a greater force
Press down on it harder
Add a little oil to the moving parts