What happens when a rocket is launched into space?
When the rocket’s engines are fired, chemical energy in the fuel is transferred to kinetic energy in the rocket.
What is work?
In the same way, if a person transfers 250J of energy,
then 250J of work is done.
This means the units for work are the same as the units
for energy – joules.
work done = energy transferred
What is the link between work and energy?
For example, if a person does 500J of work, then 500J
of energy is transferred.
How is work calculated?
The work done on an object can be calculated using this equation:
work done = force x distance moved
Distance moved is measured in meters (m).
Work done is measured in joules (j).
A cyclist peddles a bicycle with a force of
1,000N moving it 250m.
Calculating work done question 1
= 1,000 x 250
= 250,000J = 250kJ
= force x distance work
done
A truck engine moves a truck with a force of
10kN and does 500kJ
of work. How far has the truck traveled?
Calculating work done question 2
= 500,000 / 10,000
work done = force x distance
= 50m
Both these planes are about the same mass, but the jet has more powerful engines.
Power is the rate at which work is done. A more powerful engine, therefore, does work (i.e. transfers energy) faster than a less powerful engine.
What is Power?
This means that chemical energy in the fuel can be
How is power calculated?
The power exerted by an object can be calculated using the following equation:
Time is measured in seconds (s).
Power is measured in watts (W).
Work done is measured in joules (J).
work done
time taken
power =
A lawnmower engine does
10,000J of work in 10 seconds.
What is the power of the engine?
Calculating power question 1
= 1,000W
power = work done time
A car transfers
1.2 x 107 J of energy in
2 minutes. What is the power of the car?
Calculating power question 2
= 100,000W = 100kW
= 12,000,000 / 120
power = work done
time =
