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Year 7 foundation: C1.3 Melting and freezing
32 questions · 169 marks, in lesson order.
Food and fuels
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A student compares the energy in foods by burning each food under 20 cm³ of water and measuring the temperature rise.
What does the temperature rise show, and why is the comparison unfair if different masses are burned?
(2)Give two reasons the measured energy is lower than the real value, and one improvement.
(3)Total for this question: 5 marks
Food and fuels
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Two pupils burned a crisp and a piece of bread under a test tube containing 20 cm³ of water. (Illustrative data.)
| food | mass / g | temperature rise of the water / °C |
|---|---|---|
| crisp | 1 | 24 |
| bread | 2 | 9 |
Which food transferred more energy to the water?
(1)They used a 1 g crisp and a 2 g piece of bread. Explain why the comparison is not fair and how to correct it.
(2)The values are much lower than those on the food labels. Give two reasons.
(2)Total for this question: 5 marks
Energy adds up
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A device receives 600 J of energy but transfers only 420 J usefully.
Calculate the energy that is not transferred usefully. Explain why it is not destroyed.
(2)Where does this energy go? Explain what “dissipated” means.
(2)Total for this question: 4 marks
Energy adds up
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Jacquie has a mobile phone. Energy is stored in the battery of the phone.
Which energy transfer takes place in the battery as it is being charged?
(1)When the battery is fully charged, Jacquie unplugs the phone. Which energy transfers take place when the phone rings?
(1)Jacquie can change the ring-tone of her phone. The diagram shows four sound waves on an oscilloscope screen. Choose the wave that matches each description.
(3)Total for this question: 5 marks
Energy adds up
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Pupils ride a log car on a theme-park ride. The car starts from A and travels to F, where it stops by hitting a bumper. At E the car enters a trench filled with water.
At which two points does the car have no kinetic energy?
(1)and
At which point does the car have the most gravitational potential energy?
(1)At which point does the car have some kinetic energy and the least gravitational potential energy?
(1)The cars are not powered by a motor. What force causes the cars to move along the track from B to C?
(1)When a car splashes through the water at E, it slows down. What force acts on the car to slow it down?
(1)Choose from: chemical, gravitational potential, kinetic, light, sound, thermal.
(1)When the car hits the bumper at F, its energy is transferred …
Choose from: chemical, gravitational potential, kinetic, light, sound, thermal.
(2)… into energy and energy.
Total for this question: 8 marks
Energy adds up
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A garden water feature is solar-powered. The solar cell absorbs energy from the Sun and is connected to a motor in the bowl. The motor drives a pump. Water is pumped up to a jug and flows back down into the bowl.
Choose from: chemical, electrical, gravitational potential, kinetic, light, sound, thermal.
(1)The useful energy change in the solar cell is from light to energy.
Choose from: chemical, electrical, gravitational potential, kinetic, light, sound, thermal.
(1)The useful energy change in the motor is from electrical energy to energy.
Choose from: chemical, electrical, gravitational potential, kinetic, light, sound, thermal.
(2)As the water flows from the jug to the bowl, energy is changed into energy.
Give one advantage and one disadvantage of using a solar cell to power the water feature.
(2)Total for this question: 6 marks
Energy adds up
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Keith has a wind-up radio. It does not use batteries. It is powered by a steel spring. As the spring unwinds, potential energy in the spring is transferred to a generator, which turns. The generator provides electrical energy for the radio.
Complete the sentence about the generator.
(1)As the generator turns, energy is changed to electrical energy.
Complete the sentence about the speaker.
(1)In the speaker, electrical energy is changed to energy.
When Keith turns the volume up so that the radio is louder, the spring unwinds more quickly. Why?
(1)The radio also has a solar cell that can provide electrical energy. Keith takes the radio outside without changing the volume. The spring unwinds more slowly when sunlight falls on the solar cell. Explain why.
(1)The wind-up radio was designed for use in poorer countries. Suggest why wind-up radios are useful there.
(1)Total for this question: 5 marks
Energy adds up
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Caroline dives into a swimming pool. As she falls, gravitational potential energy is changed into kinetic energy.
Why does Caroline have no kinetic energy at A?
(1)| stage | total energy / kJ | gravitational potential energy / kJ | kinetic energy / kJ |
|---|---|---|---|
| A | 8 | 8 | 0 |
| B | 8 | 7 | 1 |
| C | 8 | 4 | 4 |
| D | 8 | 0 | ? |
The table shows her energy at four stages. Work out the missing kinetic energy at stage D.
(1)As Caroline falls there is no loss of energy to the air. How do the energy values for stages A, B, C and D show this?
(1)Give the name of the force that causes Caroline to speed up as she falls.
(1)Caroline takes 0.5 s to fall from A to B, from B to C and from C to D. How can you tell from the drawing that she is speeding up?
(1)When Caroline enters the water she slows down. Give the name of the force that slows her down.
(1)Total for this question: 6 marks
Energy adds up
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Jenny put a spring over a wooden rod, pressed the spring down, let go, and measured the height it reached. She repeated the experiment, pressing the spring down further each time.
Use the graph to complete the table.
(1)Pressed down 2 cm: height cm Pressed down 3 cm: height cm Pressed down 4 cm: height cm
Jenny said, “If I double the distance I press the spring down, the height it reaches will also double.” How do the results show she was wrong?
(1)The spring moves up from A (where it is released) through B to C (its highest point). Choose most, some or least for each gap. You can use each word more than once.
(1)At B it has kinetic energy and gravitational potential energy.
Choose most, some or least.
(1)At C it has gravitational potential energy and kinetic energy.
Choose most, some or least.
(1)When it stops at A it has kinetic energy and gravitational potential energy.
Total for this question: 5 marks
Energy adds up
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David uses a falling mass to split wooden logs. A 5 kg mass slides down a smooth rod and hits a metal blade. The force on the blade splits the log.
To lift the mass David uses energy stored in his muscles. Complete the energy transfer.
(1)from energy in his muscles to gravitational potential energy of the mass
The mass gains 50 J of gravitational potential energy. As it falls, what is the maximum amount of energy the mass can change from gravitational potential energy to kinetic energy?
(1)Not all the gravitational potential energy is transferred to kinetic energy as the mass falls. Give one reason for this.
(1)Give two ways David can increase the kinetic energy of the mass just before it hits the blade.
(2)David can use a different blade. Pressure = force ÷ area. Which blade puts more pressure on the log, and why?
(1)Total for this question: 6 marks
Energy and temperature
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200 g of water and 100 g of water each receive the same amount of energy.
Explain why the 200 g sample warms less. Use ideas about particles.
(5)Total for this question: 5 marks
Energy and temperature
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Two beakers contain water at 20 °C. Beaker A has 100 g of water. Beaker B has 400 g. Each is heated by an identical heater for 2 minutes.
Which beaker will have the higher temperature after 2 minutes?
(1)Explain your answer to (a)(i).
(1)A pupil says, “Temperature and energy are the same thing.” Use the beakers to explain why this is wrong.
(2)A bath of warm water at 40 °C can melt more ice than a cup of boiling water. Explain why.
(1)Total for this question: 5 marks
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