Questions: Energy

What the Activity is for

These questions can be used to explore students' ideas about energy at age 16 and address the new criteria for GCSEs in England. However, they are not intended to replace sample material from the awarding organisations. And, whilst they are set up to work as summative assessment tools, they can be used equally well for formative assessment and discussions with students.

The questions can be used for three main purposes:

• To assess a student's ability to use ideas about energy in calculations.
• To analyse physical changes.
• To construct arguments in situations where energy analysis sheds some light on decisions or activities.

What to Prepare

• Printed copies of the question sheets (see below).

What Happens During this Activity

The learning intentions of the questions have been linked to assessable learning outcomes (ALOs) and GCSE criteria where possible.

The questions review what we might expect students to be able to do with energy ideas at the end of KS4, including:

• Gravitational energy stores
• Kinetic energy stores
• Chemical energy stores
• Thermal energy stores
• efficiency calculations
• Cost calculations
• Power calculations
• Energy resources
• Energy transfer calculations
• Specific heat capacity calculations
• Work done calculations
• Insulation

The question sheets contain many multiple choice and exam-style questions. Therefore, they can be used for summative assessments, formative assessments and classroom discussions.

Some sample questions from the document are shown below.

Question: Calorie Intake/food
A cyclist has a combined mass (with her bike) of 62 kg. The mountain stage of a race involves a total climb of 1,900 m to the top where the race finishes.

(a) Which of A, B, C, or D describes the changes in the way energy is stored between the start of the climb and the end of it?

	Energy stored chemically	Energy stored gravitationally	Energy stored thermally
A	Increases	Decreases	Increases
B	Increases	Decreases	No change
C	Decreases	Increases	No change
D	Decreases	Increases	Increases

(b) Calculate the change in the energy stored gravitationally by the cyclist and her bike between the start and end points of the climb. Give your answer in MJ.

(c) In training, the cyclist has measured her total efficiency when cycling up hill to be 20%.

Calculate the change in energy stored chemically between the start and end point.

(d) It is recommended that the cyclist consumes food during the race to top up the energy stored chemically in her body. Her favourite is called ‘Energy Zap Gel’. The energy stored by one sachet is given as 365 kJ.

Calculate how many sachets she should consume during the climb.

Question answers: Calorie Intake/food
(a) D

(b) Change in gravitational potential energy
 =  mass  ×  gravitational field strength (g)  ×  height
 =  m  ×  g  ×  h  =  62 kg  ×  10 N/kg  ×  1,900 m
 =  1,178,000 J  =  1.2 MJ

(c) efficiency  =  energy stored gravitationallyenergy stored chemically  =  1.2 MJenergy stored chemically  =  20100
Energy stored chemically  =  10020  ×  1.2 MJ  =  6.0 MJ

(d) Depletion of chemical store  =  6.0 MJ
Each sachet will refill it by 365 kJ
Number of sachets  =  6.0 MJ365 kJ  =  16.4  =  17 sachets

Question: Car/train comparison
An electric train is powered by a set of electric motors. Over the duration of a journey lasting 45 minutes and covering a distance of 50 km these motors operate with a total combined average power of 920 kW.

(a) Calculate the energy transferred during the journey. Give your answer in MJ.

(b) The electricity is generated by a gas-fired power station. The network for distributing the electricity is 80% efficient. At the power station the gas plus oxygen behaves as a chemical store of energy.

Calculate by how much this chemical store has been depleted by the journey.

(c) When it is full, the train carries 480 passengers. Calculate how much the chemical store was depleted for each passenger’s journey.

(d) A small petrol powered car is used to carry a single passenger over a similar 50 km journey. The chemical store for this mode of transport is fuel plus oxygen. The chemicals store 34 MJ per litre of fuel.

During the journey the car burns 3.6 litres of fuel. Calculate how much the chemical store has been depleted by this journey.

(e) Using your answers to parts (c) and (d), discuss which type of transport, train or car, is more energy efficient in terms of transporting passengers.

Question answers: Car/train comparison
(a) Energy transferred by electrical working  =  power  ×  time
 =  920  ×  103 W  ×  (45  ×  60) s
 =  2,480 MJ

(b) efficiency  =  useful energy outputtotal energy  =  energy transferred by electrical workingenergy stored chemically  =  2,380 MJtotal energy  =  80100

energy in chemical stores  =  10080  ×  2,480 MJ  =  3,100 MJ

(c) energy per passenger  =  3,100 MJ480 passengers  =  6.46 MJ/passenger

(d) 34 MJ/litre  ×  3.6 litre  =  122 MJ. This is for one passenger.

(e) Figures indicate that a train is more efficient in terms of energy costs than a car for this journey (about 20 times);
The train would not always be full so its energy costs would be greater than the figure calculated.
The car can carry more than one person so when full the energy costs per passenger would be smaller than the figure calculated.
A full car has an energy cost approximately five times more in than a full train.

Question: When hands are rubbed together, their temperature goes up. Which of these describes the process that lead to the temperature rise?

1. Working against the frictional forces raises the surface temperature.
2. Heat is generated by friction.
3. The frictional forces convert work to heat in his hands.
4. Chemical energy is converted to heat energy.

Question answer: A

Question: An electric kettle is switched on for 1 minute. The house is supplied by a gas fired power station.
(i) Which of the following describes the changes in the way that energy is stored after the kettle has boiled compared with beforehand?

1. Electricity has been used up to increase the energy in the system.
2. Electrical energy has decreased to produce sound and heat.
3. Solar energy is used to produce electricity, which is turned into heat.
4. A chemical store has been depleted and the energy stored thermally has increased.

(ii) Which of the following describes the energy processes in the circuit?

1. Electricity produces heat in the kettle’s element.
2. The circuit transfers energy to raise the temperature of the element and water.
3. There is a chemical reaction in the element that heats the water.
4. The element creates energy, which passes into the water.

Question answers:
(i) D
(ii) B

A table that aligns the learning intentions of these questions with assessable learning outcomes, including GCSE criteria, is included in the downloadable questions below.