The High Arcal School

New Document 1
/ Name: / ______
Class: / ______
Date: / ______
Time:
Marks: / 70 marks
Comments:

ENERGY

QUESTIONS 1

Q1. A student uses an electric motor to lift a load.

In the motor, the electrical energy is transferred into other types of energy. Some of this energy is useful and the rest of the energy is wasted.

(a) (i) Name the useful energy output from the electric motor.

......

(1)

(ii) What eventually happens to the wasted energy?

......

(1)

(b) The graph shows the input energy the motor needs to lift different loads by one metre.

What can you conclude from the graph about the relationship between the load lifted and the input energy needed?

......

(2)

(c) / A shop uses escalators to lift customers to different floor levels. The escalators use electric motors. When the shop is not busy some escalators are turned off. A sign tells the customers that the escalators are turned off to save energy. /

(i) Each escalator has one motor with an average power of 4000 W. The motor is turned on for an average of 8 hours each day, 6 days each week. Electricity costs 15 pence per kilowatt-hour.

Calculate the cost of the electricity used in an average week to run one escalator.

Show clearly how you work out your answer.

......

Cost = ...... pence

(3)

(ii) Give one environmental advantage to turning off electrical appliances when they are not being used.

......

(1)

(Total 8 marks)

Q2.The image below shows a student before and after a bungee jump.

The bungee cord has an unstretched length of 20 m.

(a)For safety reasons, it is important that the bungee cord used is appropriate for the student’s weight.

Give two reasons why.

1 ......

......

2 ......

......

(2)

(b)The student jumps off the bridge.

Complete the sentences to describe the energy transfers.

Use answers from the box.

elastic potentialgravitational potentialkineticsoundthermal

Before the student jumps from the bridge he has a store of

...... energy.

When he is falling, the student's store of ...... energy increases.

When the bungee cord is stretched, the cord stores energy as

...... energy.

(3)

(c)At the lowest point in the jump when the student is stationary, the extension of the bungee cord is 35 metres.

The bungee cord behaves like a spring with a spring constant of 40 N / m.

Calculate the energy stored in the stretched bungee cord.

Use the correct equation from the Physics Equations Sheet.

......

Energy = ...... J

(2)

(Total 7 marks)

Q3.A student did an experiment to calculate her power.

The diagram below shows how she obtained the measurements needed.

The student first weighed herself and then ran up a flight of stairs. A second student timed how long it took her to go from the bottom to the top of the stairs. The height of the stairs was also measured.

(a) Complete the following sentence.

To run up the stairs the student must do work against

the force of ......

(1)

(b) The student did 2240 J of work going from the bottom of the stairs to the top of the stairs.

The student took 2.8 seconds to run up the stairs.

(i) Calculate the power the student developed when running up the stairs.

......

Power = ...... W

(2)

(ii) How much gravitational potential energy did the student gain in going from the bottom to the top of the stairs?

Tick (✔) one box.

much more than 2240 J /
2240 J /
much less than 2240 J /

(1)

The measurements taken and the calculated values for power are given in the table.

Student / Weight in newtons / Time taken in seconds / Power in watts
A / 285 / 3.8 / 240
B / 360 / 2.4 / 480
C / 600 / 3.4 / 560
D / 725 / 4.0 / 580

(i) To make a fair comparison of their powers the students kept one variable in the experiment constant.

What variable did the students keep constant?

......

(1)

(ii) From the data in the table a student wrote the following conclusion.

'The greater the weight of the student the greater the power developed.'

Suggest why this conclusion may not be true for a larger group of students.

......

(1)

(Total 6 marks)

Q4. The miners working in a salt mine use smooth wooden slides to move quickly from one level to another.

(a) A miner of mass 90 kg travels down the slide.

Calculate the change in gravitational potential energy of the miner when he moves 15 m vertically downwards.

gravitational field strength = 10 N/kg

Show clearly how you work out your answer.

......

Change in gravitational potential energy = ...... J

(2)

(b) Calculate the maximum possible speed that the miner could reach at the bottom of the slide.

Show clearly how you work out your answer.

Give your answer to an appropriate number of significant figures.

......

Maximum possible speed = ...... m/s

(3)

Explain why.

......

(3)

(Total 8 marks)

Q5.A ‘can-chiller’ is used to make a can of drink colder.

Figure 1 shows a can-chiller.

(a) The can-chiller decreases the temperature of the liquid in the can by 15 °C.
The mass of liquid is 0.33 kg.
The specific heat capacity of the liquid is 4200 J / kg °C.

Calculate the energy transferred from the liquid as it cools.

......

Energy = ...... J

(2)

(b) Complete the following sentence.

The specific heat capacity of a substance is the amount of energy required to

change the ...... of one kilogram of the

substance by one degree Celsius.

(1)

State the name of a measuring instrument used to measure mass.

......

(1)

(d) The back of the can-chiller has cooling fins, as shown in Figure 2.

The cooling fins increase the rate of energy transfer from the can-chiller to the surroundings.

Complete the following sentences.

The cooling fins are a ...... colour because that makes them

good emitters of infrared radiation.

The large surface area of the cooling fins allows the air around the can-chiller

to gain energy quickly and rise, transferring energy by ......

(2)

(e) (i)The energy input to the can-chiller is the same as the energy output. This shows that energy is conserved.

Complete the following sentence.

Energy can be transferred usefully, stored or dissipated, but cannot be

...... or destroyed.

(1)

(ii)The temperature of the can of drink decreases while it is in the can-chiller.

What happens to the temperature of the air around the cooling fins?

......

(1)

(Total 8 marks)

Q6.A ‘can-chiller’ is used to make a can of drink colder.

The image below shows a can-chiller.

(a) The initial temperature of the liquid in the can was 25.0 °C.
The can-chiller decreased the temperature of the liquid to 20.0 °C.
The amount of energy transferred from the liquid was 6930 J.
The mass of liquid in the can was 0.330 kg.

Calculate the specific heat capacity of the liquid.

Give the unit.

......

Specific heat capacity = ...... unit ......

(4)

(b) Energy is transferred through the metal walls of the can of drink by conduction.
Explain how.

......

(4)

(c) The energy from the can of drink is transferred to the air around the can-chiller.
A convection current is set up around the can-chiller. Explain how.

......

(3)

(d) The can-chiller has metal cooling fins that are designed to transfer energy quickly to the surroundings.

Give two features that would help the metal cooling fins to transfer energy quickly to the surroundings.

1......

2......

(2)

(Total 13 marks)

Q7. A wood burning stove is used to heat a room.

Photograph supplied by iStockphoto/Thinkstock

The fire in the stove uses wood as a fuel. The fire heats the matt black metal case of the stove.

(a) The air next to the stove is warmed by infrared radiation.

How does the design of the stove help to improve the rate of energy transfer by infrared radiation?

......

(2)

(b) Burning 1 kg of wood transfers 15 MJ of energy to the stove. The stove then transfers 13.5 MJ of energy to the room.

Calculate the efficiency of the stove.

Show clearly how you work out your answer.

......

Efficiency = ......

(2)

(c) Some of the energy from the burning wood is wasted as the hot gases leave the chimney and warm the air outside the house.

Name one other way energy is wasted by the stove.

......

(1)

(d) Some people heat their homes using electric heaters. Other people heat their homes using a wood burning stove.

Give two environmental advantages of using a wood burning stove to heat a home rather than heaters that use electricity generated from fossil fuels.

1 ......

......

2 ......

......

(2)

(e) The metal case of the stove gets hot when the fire is lit.

Here is some information about the stove.

Mass of metal case / 100 kg
Starting temperature of metal case / 20 °C
Final temperature of metal case / 70 °C
Specific heat capacity of metal case / 510 J/kg °C

Calculate the energy required to raise the temperature of the metal case to 70 °C.

Show clearly how you work out your answer and give the unit.

......

Energy required = ......

(3)

(Total 10 marks)

Q8.A student finds some information about energy-saving light bulbs.

(a) A 30W light bulb uses 600J of electrical energy in a certain period of time. In that time, it produces 450 J of light energy. The rest of the energy is wasted.

(i)Calculate the energy wasted by the light bulb in this period of time.

......

Wasted energy = ...... J

(1)

(ii)What happens to the energy wasted by the light bulb?

......

(1)

(iii)Calculate the efficiency of this light bulb.

......

Efficiency = ......

(2)

(iv)Calculate the period of time, in seconds, during which the 600 J is provided to the 30W light bulb.

......

Time = ...... s

(2)

(b) A company that makes light bulbs provides information about some of their products.

The table shows some of this information.

Power in watts / Lifetime in hours / Cost of bulb in £
Filament bulb / 60 / 1250 / 2.00
LED bulb / 12 / 50 000 / 16.00

(i)Suggest why it is important to confirm this information independently.

......

(1)

(ii)A homeowner is thinking about replacing his filament bulbs with LED bulbs.

A 12 W LED bulb gives the same light output as a 60 W filament bulb.

Suggest reasons why the homeowner is likely to choose LED bulbs.

Use the information given in the table.

......

(2)

(iii)State one factor, other than efficiency, that is important when considering the choice of a bulb for lighting in the home.

......

(1)

(Total 10 marks)

M1.(a)(i) kinetic (energy)

allow gravitational potential (energy) / gpe

movement is insufficient

(ii) dissipates into the surroundings

allow warms up the surroundings / air / motor

accept lost to the surroundings

accept lost as heat

ignore reference to sound

it is lost is insufficient

(b) energy (required) increases with load

accept positive correlation

do not accept (directly) proportional

further amplification eg increases slowly at first (or up to 4 / 5 N), then increases rapidly

simply quoting figures is insufficient

an answer that only describes the shape of the line gains no marks

2880

accept £28.80 for all 3 marks

an answer £2880 gains 2 marks

allow 1 mark for obtaining 48 h or converting to kW

allow 2 marks for correct substitution

ie 4 × 48 × 15

note: this substitution may be shown as two steps

an answer 2 880 000 gains 2 marks

an answer £4.80 / 480 gains 2 marks

an answer of 192 (ie calculation of energy without subsequent calculation of cost) gains 1 mark)

(ii) any sensible suggestion eg

conserves fossil fuels

less (fossil) fuels burned

less pollutant gas (produced)

accept a named pollutant gas

less greenhouse gas (produced)

saves energy is insufficient

[8]

M2.(a)any two from:

•bungee rope may snap

•rope may extend too much

•student may land in the river

(b)gravitational potential

correct order only

kinetic

elastic potential

(c)½ × 40 × 352

24 500 (J)

accept 25 000 (J) (2 significant figures)

allow 24 500 (J) with no working shown for 2 marks

[7]

M3.(a) gravity

accept weight for gravity

air resistance is insufficient

(b) (i) 800

allow 1 mark for correct substitution ie

provided no subsequent step

(ii) 2240 J

accept (height of) stairs

(ii) a fast / short time (for a lighter student) may give the greatest power

accept time is a factor

a slow / long time (for a heavy student) may give the least power

fitness is insufficient

[6]

M4.(a) 13 500 (J)

allow 1 mark for correct substitution, ie 90 x 10 x 15 provided no subsequent step shown

(b) 17or

correctly calculated and answer given to 2 or 3 significant figures

accept 17.3

allow 2 marks for an answer with 4 or more significant figures, ie 17.32

allow 2 marks for correct substitution, ie 13 500/ their (a) = ½ x 90 x v2

allow 1 mark for a statement or figures showing KE = GPE

(against) friction (between the miner and slide)

accept ‘air resistance’or‘drag’ for friction

(due to the) slide not (being perfectly) smooth

accept miners clothing is rough

causing (kinetic) energy to be transferred as heat/internal energy of surroundings

accept lost/transformed for transferred

accept air for internal energy of surroundings

[8]

M5.(a) 20 790 (J)

an answer of 21 000 (J) (2 s.f.) gains 2 marks

allow 1 mark for correct
substitution:
ie E = 0.33 × 4200 × 15 provided no subsequent step shown

(b) temperature

accept scales

do not accept a scale
do not accept weighing scales
do not accept newtonmeter
do not accept spring balance

(d) dark / black / (dark) grey

convection

correct order only

(e) (i)created

accept made

(ii)increases

[8]

M6.(a) 4200

allow 2 marks for correct substitution
ie 6930 = 0.330 × c × 5.0

answers of 1050 or 840

correctly calculated answer from correct substitution of incorrect temperature change

identification of temperature change ie 5 °C
gain 1 mark

J / kg°C

accept J / kg K

(b) (in a metal) free electrons

to gain full credit the answer must be in terms of free electrons

gain kinetic energy

accept move faster

(free electrons) transfer energy to other electrons / ions / atoms

do not accept particles

by collision

allow a maximum of 2 marks for answers in terms of atoms / ions / particles

•gaining kinetic energy or vibrating faster / more

•transferring energy by collisions

(which causes the) air to become less dense / expand

do not accept particles become less dense

(so the) warm air rises

do not accept heat rises
particles rise is insufficient

(d) large surface area

ignore references to type of metal or external conditions

black / dark (colour)

[13]

M7. (a)any two from:

• black is a good emitter of (infrared radiation)

accept heat for radiation

ignore reference to absorbing radiation

• large surface (area)

• matt surfaces are better emitters (than shiny surfaces)

accept matt surfaces are good emitters

ignore reference to good conductor

(b)90% or 0.9(0)

allow 1 mark for correct substitution, ie

provided no subsequent step shown

an answer of 90 scores 1 mark

an answer of 90 / 0.90 with a unit scores 1 mark

(c)(producing) light

allow (producing) sound

(d)any two from:

• wood is renewable

accept wood grows again / quickly
accept wood can be replanted

• (using wood) conserves fossil fuels

accept doesn’t use fossil fuels

• wood is carbon neutral

accept a description

cheaper / saves money is insufficient

(e)E = m × c × θ

2 550 000

allow 1 mark for correct substitution
ie 100 × 510 × 50
provided no subsequent step shown

answers of 1 020 000, 3 570 000 gain 1 mark

joules /J

accept kJ / MJ

do not accept j

for full credit the unit and numerical answer must be consistent

[10]

M8.(a) (i)150

(ii)transferred to the surroundings by heating

reference to sound negates mark

(iii)0.75

450 / 600 gains 1 mark

accept 75% for 2 marks

maximum of 1 mark awarded if a unit is given

(iv)20 (s)

correct answer with or without working gains 2 marks

correct substitution of 600 / 30 gains 1 mark

(b) (i)to avoid bias

(ii)use less power and last longer

1 LED costs £16, 40 filament bulbs cost £80

filament costs (5 times) more in energy consumption

(iii)any one from:

•availability of bulbs

•colour output

•temperature of bulb surface

[10]

Page 1