Energy - Section B - Maths questions

Don't forget to take a ruler and calculator into the exam.

Maths questions often start with the command words like calculate, determine, estimate and measure. They will then include blank space for you to show your working.

When an answer to a maths question is marked:

  • full marks are given for the right answer (but it's wise to show your working so you can check your answer)
  • marks are given for working, including substitution and rearrangement
  • errors carried forward are taken into account

Errors carried forward is to do with what happens if a later answer depends on an earlier answer, and you get the earlier one wrong. You could still get full marks in the later answer if your working is correct but you use the incorrect earlier answer.

If your answer has many decimal places or figures, make sure you give it to an appropriate number of decimal places or significant figures. You may be asked to give units. This may earn you an additional mark, so don't forget to check whether you need to do this.

Some maths questions might ask you to plot or complete a graph or table. When you draw a graph, make sure you:

  1. plot each point accurately
  2. draw a best fit straight line or curve

You may be given a grid with axes and scales already given. Sometimes you may be given an empty grid for you to supply your own axes. You should:

  • put the independent variable on the x-axis and the dependent variable on the y-axis
  • make sensible scales so that the plotted points cover at least 50% of the area of the graph
  • label the axes with their quantity and unit, eg time (s)

Sample question 1 - Foundation

Question

A car on a rollercoaster is stationary at the top of a slope.

It has a weight of 6,500 N and a potential energy of 217,000 J.

Calculate how high above the ground it is. [2 marks]

OCR Gateway Science, GCE Physics, Paper J249, 2016.

Rearrange: work = force × distance [1]

so, distance = work / force = 217,000 ÷ 6,500 = [1]

Sample question 2 - Foundation

Question

An oil-filled heater in a room produces 800 J of energy each second.

a) Calculate the energy produced by the heater in 10 minutes. [2 marks]

b) Enough energy is supplied to raise the heater's temperature by 40°C, but it only heats up to 32°C. Suggest two reasons why. [2 marks]

OCR Gateway Science, GCE Physics, Paper J249, 2016.

a) Time conversion: 10 × 60 = 600 s [1]

800 × 600 = 480,000 J [1]

b) Any two from:

  • some energy used to heat the radiator case (rather than the oil inside)
  • energy passed from oil to air in room/oil undergoes cooling whilst heating up
  • energy is dissipated to surroundings
  • it is not 100% efficient at transferring energy

[2]

Sample question 3 - Higher

Question

Alex has two fire places in her home (X and Y) shown in the diagrams below.

Two fireplaces, one is directly connected to a chimney, the other is connected to a heat exchanger before its energy is output through the chimney.

Why does Fire Y help save money on the energy bills for her home?

Use calculations of efficiency in your answer. [4 marks]

OCR Gateway Science, GCE Physics, Paper J249, 2016 - Higher.

Fire Y helps save money because half of the (previously) wasted power or energy/0.5 kw is being used to heat water. [1]

Less energy needed from other sources to heat water. [1]

Fire X is (4/5 × 100%) = 80% efficient [1]

Fire Y is (4.5/5 × 100%) = 90% efficient [1]

Sample question 4 - Higher

Question

A rocket carrying a vehicle called the Mars Rover was sent to Mars.

The Mars Rover has a mass of 185 kg.

The gravitational field strength (g) on Mars is 3.75 N/kg.

Calculate the weight of the Rover vehicle on Mars.

Show your working and give your answer to 3 significant figures.

State the unit for weight. [5 marks]

OCR Gateway Science, GCE Physics, Paper J249, 2016.

weight = mass × gravitational field strength [1]

weight = 185 × 3.75 [1]

= 693.75 [1]

= 694 to 3 significant figures [1]

= 694 N [1]