Work Done (Oxford AQA IGCSE Physics)

Worked Example

A car moving at speed begins to apply the brakes. The brakes of the car apply a force of 500 N which brings it to a stop after 23 m.

Calculate the work done by the brakes in stopping the car. 

Answer:

Step 1: List the known quantities

• Distance, d = 23 m

• Force, F = 500 N

Step 2: Write out the equation relating work, force and distance

W = F × d 

Step 3: Calculate the work done on the car by the brakes

W = 500 × 23

W = 11 500 J

Worked Example

A meteorite travels at a constant speed through the vacuum of space. When it reaches Earth's atmosphere it burns up.

Describe the energy transfers taking place that cause the meteorite to burn as it enters the Earth's atmosphere.

Answer:

Step 1: Identify the initial store of energy

• The meteorite is moving through space, therefore it has energy in its kinetic store

Step 2: Identify the energy transfer pathway

• When the meteorite enters Earth's atmosphere, it experiences frictional forces due to air resistance, therefore energy is transferred by heating

Step 3: Describe the energy transfer

• Energy is transferred from the kinetic store of the meteorite to the thermal store of the meteorite and the thermal store of the air particles

• The energy transferred by heating is great enough for the meteorite to burn up