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KS3 · Physics

K13 Energy

AQA KS3 National Curriculum - Energy (AQA-style question conventions) · Calculator allowed · about 65 minutes

Name: _______________________________ Date: ____ / ____ / ______

Answer ALL questions. Show all your working.

For each situation, name the main energy store involved. Choose from: kinetic, gravitational potential, elastic potential, chemical, thermal.

(a)A stretched trampoline spring, just before a gymnast is released upwards.(1)

(b)A skydiver falling at a constant, high speed.(1)

(c)A full can of petrol, before it is burned in an engine.(1)

(d)A cup of tea, just after it has been made with boiling water.(1)

An electric kettle heats water until it boils.

(a)State the useful energy transfer pathway that occurs when the kettle heats the water.(2)

(b)State one way that energy is wasted from the kettle to the surroundings.(1)

Use the Physics Equations Sheet: KE = 1/2 x m x v^2. A car of mass 800 kg is travelling at a speed of 20 m/s.

(a)Calculate the kinetic energy store of the car. Give your answer in joules.(2)

(b)Write your answer to part (a) in kilojoules (kJ).(1)

Use the Physics Equations Sheet: GPE = m x g x h, where g = 10 N/kg. A ball of mass 0.5 kg is lifted to a height of 2.5 m above the ground.

(a)Calculate the gravitational potential energy store of the ball.(2)

(b)The ball is released and falls freely (ignore air resistance). State what happens to this gravitational potential energy store as the ball falls.(1)

The ball in Question 4 falls freely from rest and air resistance can be ignored. Use the Physics Equations Sheet: KE = 1/2 x m x v^2. Show that the speed of the ball just before it hits the ground is about 7 m/s.

(4)

Use the Physics Equations Sheet: efficiency = (useful output energy transferred / total input energy transferred) x 100. A filament lamp is supplied with 100 J of electrical energy. Only 20 J is usefully transferred as light; the rest is wasted, mostly as heat.

(a)Calculate the efficiency of the lamp.(2)

(b)State one reason why the efficiency of the lamp is less than 100%.(1)

Use the Physics Equations Sheet: P = E / t. An electric motor transfers 1200 J of energy in 30 s.

(a)Calculate the power of the motor.(2)

A mobile phone charger has a total power input of 12 W. Of this, 9 W is usefully transferred to the phone battery's chemical energy store. The rest is wasted, mostly heating the charger casing.

(a)Calculate the wasted power output of the charger.(1)

(b)Use the Physics Equations Sheet: efficiency = (useful output energy transferred / total input energy transferred) x 100. Calculate the efficiency of the charger.(2)

(c)Suggest one change to the charger's design that would reduce the amount of wasted energy.(1)

Use the Physics Equations Sheet: energy transferred (kWh) = power (kW) x time (hours). An electric heater has a power rating of 2 kW and is switched on for 3 hours. Electricity costs 28p per kWh.

(a)Calculate the number of kWh of energy transferred by the heater.(2)

(b)Calculate the total cost of running the heater for the 3 hours.(2)

Complete the table by classifying each energy resource as 'renewable' or 'non-renewable'.

(a)Solar(1)

(b)Wind(1)

(c)Natural gas(1)

(d)Coal(1)

(e)Biomass(1)

(f)Nuclear fuel (uranium)(1)

The UK generates electricity using both wind turbines and coal-fired power stations. Evaluate the use of wind power compared with coal power for generating the UK's electricity. In your answer, consider reliability, cost and environmental impact.

(6)

Required practical: A student investigates how the type of insulating material affects the rate of cooling of hot water. She wraps identical beakers in different materials (cotton wool, bubble wrap, and no insulation as a control), fills each beaker with 200 cm³ of water at 80 degrees C, fits a lid with a hole for a thermometer, and records the temperature every 2 minutes for 10 minutes.

(a)Identify the independent variable in this investigation.(1)

(b)Identify the dependent variable in this investigation.(1)

(c)State two variables that the student should keep the same to make this a fair test.(2)

(d)Suggest one reason why the student used a lid with a small hole for the thermometer on each beaker.(2)

(e)The water in the beaker with no insulation cooled from 80 degrees C to 50 degrees C over the 10 minutes. Calculate the mean rate of cooling, in degrees C per minute.(3)

(f)Suggest one improvement the student could make to increase the reliability of her results.(2)

Using the method described in Question 12, the student obtained these results for water starting at 80 degrees C after 10 minutes: cotton wool = 62 degrees C, bubble wrap = 68 degrees C.

(a)Calculate the mean rate of cooling for the cotton wool.(2)

(b)Calculate the mean rate of cooling for the bubble wrap.(2)

(c)State which material is the better insulator, using your answers to parts (a) and (b).(2)

(d)Explain, in terms of particles, why bubble wrap reduces the rate of energy transfer from the water compared with cotton wool alone.(2)

State the main method of thermal energy transfer (conduction, convection or radiation) taking place in each example.

(a)A metal spoon left in a hot pan of soup gets hot.(1)

(b)Water in a pan circulates as it heats up towards boiling.(1)

(c)You feel warmth from a bonfire without touching it.(1)

(d)Warm air rises above a hot radiator and circulates around a room.(1)

Use the Physics Equations Sheet: change in thermal energy = mass x specific heat capacity x change in temperature (E = m x c x change in T). The specific heat capacity of water is 4200 J/(kg degrees C).

(a)Calculate the energy needed to heat 2 kg of water by 20 degrees C.(2)

(b)Write your answer to part (a) in kilojoules (kJ).(1)

Use the Physics Equations Sheet: E = P x t. A 60 W lamp is left switched on for 5 hours. A 2 kW kettle is switched on for 6 minutes. Show that the lamp transfers more total energy than the kettle.

(5)

Which of these is a non-renewable fossil fuel?

(a)Choose the correct answer.(1)

A) Solar
B) Wind
C) Natural gas
D) Hydroelectric

Use the Physics Equations Sheet: P = E / t. A student transfers 3000 J of energy in their kinetic and gravitational potential energy stores when climbing a flight of stairs. Running up the stairs takes 5 s. Walking up the same flight of stairs takes 15 s.

(a)Calculate the student's power output when running up the stairs.(2)

(b)Calculate the student's power output when walking up the stairs.(2)

(c)The same amount of energy, 3000 J, is transferred in both cases. Explain why the student's power output is greater when running.(2)

In a particular year, the UK's electricity was generated from these sources: natural gas 40%, wind 25%, nuclear 15%, solar 5%, biomass 5%, coal 5%, other sources 5%.

(a)Calculate the total percentage of the UK's electricity that came from renewable sources (wind, solar and biomass only).(2)

(b)Suggest one advantage and one disadvantage of increasing the percentage of UK electricity generated from wind power.(2)

Mark scheme · K13 Energy

Question 1

(a) B1 elastic potential (energy store) cao
(a) Answer: Elastic potential energy store
(b) B1 kinetic (energy store) cao
(b) Answer: Kinetic energy store
(c) B1 chemical (energy store) cao
(c) Answer: Chemical energy store
(d) B1 thermal (energy store) cao
(d) Answer: Thermal energy store

Question 2

(a) B1 energy is transferred electrically (from the mains/electrical energy store)
(a) B1 to the thermal energy store of the water oe
(a) Answer: Electrical energy is transferred to the thermal energy store of the water.
(b) B1 thermal energy transferred (by heating) to the surroundings through the kettle body/lid oe
(b) Answer: Energy is transferred by heating to the surrounding air through the body of the kettle.

Question 3

(a) M1 correct substitution: KE = 0.5 x 800 x 20²
(a) A1 160000 J cao (allow 1.6 x 10⁵ J)
(a) Answer: 160000 J
(b) B1 160 kJ ft from (a)
(b) Answer: 160 kJ

Question 4

(a) M1 correct substitution: GPE = 0.5 x 10 x 2.5
(a) A1 12.5 J cao
(a) Answer: 12.5 J
(b) B1 transferred to the kinetic energy store (of the ball) oe
(b) Answer: It is transferred to the ball's kinetic energy store.

Question 5

M1 recognise energy conservation: KE at bottom = GPE at top (= 12.5 J, ft from Q4a)
M1 rearrange KE = 1/2 x m x v² to make v the subject: v = √2 x KE / m
A1 correct substitution and evaluation: v = √2 x 12.5 / 0.5 = √50
A1 v = 7.1 m/s (2 s.f.), consistent with the given value of about 7 m/s cso
Answer: v = 7.1 m/s (approximately 7 m/s)

Question 6

(a) M1 correct substitution: (20 / 100) x 100
(a) A1 20% cao
(a) Answer: 20%
(b) B1 energy is wasted/dissipated (as heat) to the surroundings oe
(b) Answer: Energy is wasted as heat to the surroundings.

Question 7

(a) M1 correct substitution: P = 1200 / 30
(a) A1 40 W cao
(a) Answer: 40 W

Question 8

(a) B1 3 W cao
(a) Answer: 3 W
(b) M1 correct substitution: (9 / 12) x 100
(b) A1 75% cao
(b) Answer: 75%
(c) B1 any sensible design change, e.g. use more efficient electrical components, improve insulation of the casing, reduce resistance in the circuit oe
(c) Answer: Example: use lower-resistance components/wiring so less energy is wasted as heat.

Question 9

(a) M1 correct substitution: 2 x 3
(a) A1 6 kWh cao
(a) Answer: 6 kWh
(b) M1 correct substitution: 6 x 28 (ft from a)
(b) A1 168p or GBP 1.68 cao
(b) Answer: GBP 1.68

Question 10

(a) B1 renewable cao
(a) Answer: Renewable
(b) B1 renewable cao
(b) Answer: Renewable
(c) B1 non-renewable cao
(c) Answer: Non-renewable
(d) B1 non-renewable cao
(d) Answer: Non-renewable
(e) B1 renewable cao
(e) Answer: Renewable
(f) B1 non-renewable cao
(f) Answer: Non-renewable

Question 11

Level 1 (1-2): Simple statements are made about wind and/or coal power, with limited or no comparison. Points may be isolated and not clearly linked to reliability, cost, or environmental impact.
Level 2 (3-4): A description of some relevant features of wind and coal power is given, with some comparison between them. At least two of reliability, cost, and environmental impact are addressed, though the argument may be one-sided or incomplete.
Level 3 (5-6): A clear, balanced evaluation is given, comparing wind and coal power across reliability, cost, and environmental impact, leading to a justified overall conclusion.
Indicative content:
- Wind power is renewable and produces no carbon dioxide during generation; coal is non-renewable and produces carbon dioxide and other pollutants when burned, contributing to climate change and poorer air quality
- Wind power is unreliable because output depends on wind speed; there is no electricity generated when there is no wind, and turbines can be shut down in very high winds
- Coal power stations can generate electricity reliably on demand, regardless of weather, and can be scaled up quickly to meet peak demand
- Wind turbines have relatively high initial construction costs but very low running costs (no fuel to buy); coal stations have lower construction costs but ongoing fuel costs and are subject to fluctuating coal prices
- Wind farms can have a visual and noise impact on the landscape and may affect local wildlife (for example birds); coal mining and burning can cause land damage and long-term environmental harm
- A balanced electricity supply may use a mix of both, or increasingly renewables backed up by storage or other reliable sources, to balance reliability with environmental impact
- Conclusion should weigh the long-term environmental benefits of wind power against the reliability advantages of coal, coming to a justified overall judgement

Question 12

(a) B1 the type of insulating material (used to wrap the beaker) cao
(a) Answer: Type of insulating material
(b) B1 the temperature of the water (measured over time) cao
(b) Answer: Temperature of the water
(c) B1 any one of: volume/mass of water, starting temperature of water, size/shape/material of beaker, room temperature, time between readings, thickness of insulation
(c) B1 a second, different valid control variable from the list above
(c) Answer: Any two of: volume of water, starting temperature, size of beaker, room temperature, time between readings.
(d) B1 reduces energy loss from the surface of the water by evaporation/convection oe
(d) B1 so that the comparison between the different insulating materials is fair/valid oe
(d) Answer: The lid reduces energy loss by evaporation and convection from the open top, keeping the comparison between materials fair.
(e) M1 correct temperature change: 80 - 50 = 30 (degrees C)
(e) M1 correct division by time: 30 / 10
(e) A1 3.0 degrees C per minute cao
(e) Answer: 3.0 degrees C per minute
(f) B1 repeat the experiment for each material (and calculate a mean) oe
(f) B1 take readings more frequently/use a data logger to reduce timing or reading error oe
(f) Answer: Repeat the test for each material and calculate a mean rate of cooling; alternatively use a data logger for more frequent, more precise readings.

Question 13

(a) M1 correct working: (80 - 62) / 10
(a) A1 1.8 degrees C per minute cao
(a) Answer: 1.8 degrees C per minute
(b) M1 correct working: (80 - 68) / 10
(b) A1 1.2 degrees C per minute cao
(b) Answer: 1.2 degrees C per minute
(c) B1 bubble wrap ft from (a) and (b)
(c) B1 because it has the lower/smaller rate of cooling oe
(c) Answer: Bubble wrap, because it has the lower rate of cooling (1.2 versus 1.8 degrees C/min).
(d) B1 bubble wrap traps pockets/layers of air oe
(d) B1 air is a poor conductor of thermal energy, so this reduces energy transfer by conduction oe
(d) Answer: Bubble wrap traps pockets of air, and air is a poor conductor, so less thermal energy is conducted away from the water.

Question 14

(a) B1 conduction cao
(a) Answer: Conduction
(b) B1 convection cao
(b) Answer: Convection
(c) B1 radiation (infrared radiation) cao
(c) Answer: Radiation
(d) B1 convection cao
(d) Answer: Convection

Question 15

(a) M1 correct substitution: 2 x 4200 x 20
(a) A1 168000 J cao
(a) Answer: 168000 J
(b) B1 168 kJ ft from (a)
(b) Answer: 168 kJ

Question 16

M1 convert lamp time to seconds: 5 x 3600 = 18000 s (or work consistently in hours)
A1 lamp energy = 60 x 18000 = 1080000 J (or 1.08 MJ, or 0.3 kWh)
M1 convert kettle time to seconds: 6 x 60 = 360 s (or work consistently in hours)
A1 kettle energy = 2000 x 360 = 720000 J (or 0.72 MJ, or 0.2 kWh)
A1 correct comparison and conclusion: 1080000 J > 720000 J, so the lamp transfers more total energy cso
Answer: Lamp = 1080000 J, kettle = 720000 J; the lamp transfers more energy overall.

Question 17

(a) B1 C cao
(a) Answer: C) Natural gas

Question 18

(a) M1 correct substitution: 3000 / 5
(a) A1 600 W cao
(a) Answer: 600 W
(b) M1 correct substitution: 3000 / 15
(b) A1 200 W cao
(b) Answer: 200 W
(c) B1 power is the rate of energy transfer (energy transferred per second) oe
(c) B1 the same energy is transferred in a shorter time when running, so the rate of energy transfer (power) is greater oe
(c) Answer: Power is the rate of energy transfer; since the same energy is transferred in less time when running, the rate (power) is higher.

Question 19

(a) M1 correct addition: 25 + 5 + 5
(a) A1 35% cao
(a) Answer: 35%
(b) B1 advantage: renewable/will not run out, or produces no carbon dioxide during generation oe
(b) B1 disadvantage: unreliable/depends on wind speed, cannot be increased on demand, or visual/noise impact oe
(b) Answer: Advantage: it does not produce carbon dioxide while generating electricity. Disadvantage: it is unreliable because output depends on wind speed.

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