An electric current transfers energy from the battery to the filament lamp.
State the two energy transfer pathways for the energy emitted by the filament lamp.
State which store of energy in the battery is decreasing.
Explain how the principle of conservation of energy applies to this circuit.
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A drone is a machine that can fly. Fig. 4.1 shows a drone rising into the air, lifting a camera.
The drone obtains energy from a battery of cells.
Complete the sequence of useful energy transfers as the drone rises into the air. One part is done for you.
................................. store → kinetic store → ............................. store
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The drone can move in any direction up or down, backwards or forwards, left or right. It can also remain stationary above the ground.
Describe the motion and position of the drone when it has both a large quantity of potential energy and a small quantity of kinetic energy.
When the drone moves, it wastes some energy.
Describe what happens to this energy.
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A bouncy ball is dropped from a height of 1.65 m onto a smooth wooden floor, where it bounces, reaching a height of 1.43 m.
The bouncy ball has a mass of 0.07 kg
Complete the energy transfers taking place when
(i) the ball is falling towards the floor
.................................... energy store → kinetic energy store [1]
(ii) the ball hits the floor and deforms
kinetic energy store → .................................... energy store [1]
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Calculate the energy in the gravitational potential store of the ball just before it is dropped.
energy = ....................................
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Calculate the speed at which the bouncy ball hits the floor.
For the purposes of this calculation, you can assume there is no air resistance.
speed = ....................................
The bounce height is smaller than the height the ball was dropped from.
Explain why this is the case.
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Identify the unit for energy.
Tick one box.
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N
K
J
State why work done is equal to energy transferred.
Fork-lift trucks are used to move crates in warehouses. Fig. 1.1 shows a crate being lifted to high shelf.
Fig. 1.1
The fork-lift truck lifts a crate of 450 N to a shelf that is 3.9 m above the ground.
Calculate the work done to lift the crate.
work done = ....................................
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The total energy input for the fork-lift truck to lift the crate is 2500 J
Calculate the efficiency of the fork-lift truck.
efficiency = ....................................
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A group of students want to measure their power output when climbing a ladder.
Student A has a mass of 54 kg and takes 15 s to climb the ladder which has a vertical height of 1.8 m.
Calculate the work done in raising the student's body mass as they climb the ladder.
work = ....................................
Calculate the power output of Student A in raising their body mass up the ladder.
power output = ....................................
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Student A's body is only 17% efficient when climbing the ladder.
Calculate the total power input of the student to climb the ladder.
power input = ....................................
State the energy transfer taking place as student A climbs the ladder.
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Fig. 3.1 shows a model of a wind turbine used to demonstrate the use of wind to generate electricity. The wind is blowing towards the model, as shown.
The mass of air passing through the circular area swept out by the turbine blades each second is 7.5 kg. The energy in the kinetic store of the air that passes through this circular area each second is 240 J.
(i) Calculate the speed of the air.
speed = ........................................................ [3]
(ii) The moving air drives a generator. State the input power of the air passing through the turbine blades.
input power = ........................................................ [1]
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The output current of the generator is 2.0 A. The output potential difference (p.d.) of the generator is 11 V.
(i) Calculate the output power of the generator.
output power = ........................................................ [2]
(ii) Calculate the efficiency of the wind turbine.
efficiency = .................................................... % [2]
The density of air is 1.3 kg / m3.
Calculate the volume of air passing through the circular area swept out by the turbine blades each second.
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A force is used to move an object from the Earth’s surface to a greater height.
Explain why the energy in the gravitational potential store of the object increases.
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Fig. 2.1 shows a train moving up towards the top of a mountain.
The train transports 80 passengers, each of average mass 65 kg, through a vertical height of 1600 m.
Calculate the increase in energy stored in the gravitational potential store of the passengers.
increase in energy = .........................................................
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The engine of the train has a power of 1500 kW. The time taken to reach the top of the mountain is 30 minutes.
Calculate the efficiency of the engine in raising the 80 passengers 1600 m to the top of the mountain.
efficiency = .........................................................
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State what is meant by the principle of conservation of energy.
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Fig. 3.1 shows a girl throwing a heavy ball.
(i) State the energy transfers that take place from when the girl begins to exert a force on the ball until the ball hits the ground and stops moving.
[2]
(ii) The mass of the ball is 4.0 kg. The girl exerts a force on the ball for 0.60 s. The speed of the ball increases from 0 m/ s to 12 m/s before it leaves the girl’s hand.
Calculate:
the momentum of the ball on leaving the girl’s hand
momentum = ...........................................................[2]
the average resultant force exerted on the ball.
average resultant force = ...........................................................[2]
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Fig. 3.1 shows an aircraft on the deck of an aircraft carrier.
The aircraft accelerates from rest along the deck. At take-off, the aircraft has a speed of 75 m/s.
The mass of the aircraft is 9500 kg.
Calculate the energy in the kinetic store of the aircraft at take-off.
energy = ...........................................................
On an aircraft carrier, a catapult provides an accelerating force on the aircraft. The catapult provides a constant force for a distance of 150 m along the deck.
Calculate the resultant force on the aircraft as it accelerates. Assume that all of the kinetic energy at take-off is from the work done on the aircraft by the catapult.
force = ...........................................................
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An electric kettle contains water at a temperature of 19 °C. The kettle has a power rating of 3.0 kW and is switched on for 3.5 minutes.
Calculate the energy supplied to the kettle by the electricity supply.
energy = ........................................................
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At 3.5 minutes, the temperature of the water reaches 100 °C. The volume of the water in the kettle is 1700 cm3 and its density is 1.0 g/cm3. The specific heat capacity of water is 4200 J/(kg °C).
Calculate the energy gained by the water.
energy = ........................................................
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Calculate the efficiency of the kettle.
efficiency = ........................................................
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Fig. 2.1 shows a fork-lift truck lifting a box.
The electric motor that drives the lifting mechanism is powered by batteries.
Name the store that energy is usefully transferred from by the batteries.
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The lifting mechanism raises a box of mass 32 kg through a vertical distance of 2.5 m in 5.4 s.
(i) Calculate the energy transferred to the gravitational potential energy store of the box.
energy = ...........................................................[2]
(ii) The efficiency of the lifting mechanism is 0.65 (65%).
Calculate the input power to the lifting mechanism.
input power = ...........................................................[3]
Batteries are recharged from a mains voltage supply that is generated in an oil-fired power station.
By comparison with a wind farm, state one advantage and one disadvantage of running a power station using oil.
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A man is working on a platform. He uses a rope to raise a bag from the ground to the platform as shown in Fig. 4.1.
(i) Name the energy store that energy is usefully transferred to as the bag is lifted at constant speed.
[1]
(ii) The man then lifts a second bag from the ground to the platform. The first bag weighs 100 N and the second bag weighs 150 N.
On which bag of materials does the man do more work?
Explain your answer.
[1]
(iii) The man wants to determine his useful power as he lifts one of the bags. He knows the weight of the bag. State the two other quantities he needs to know.
[2]
The statements describe processes in a coal-fired power station. They are not in the correct order.
A Energy is transferred to the thermal store of the water
B Coal burns releasing energy from its chemical store
C Energy is transferred electrically via the national grid
D A turbine turns coils in a magnetic field
E Steam turns a turbine
Use the letters A, B, C, D and E to complete the flow chart explaining how the power station works.
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A rifle fires a bullet of mass 0.020 kg vertically upwards through the air. As it leaves the rifle, the speed of the bullet is 350 m/s.
Calculate
(i) the energy in the kinetic store of the bullet as it leaves the rifle,
energy = ...........................................................[3]
(ii) the maximum possible height that the bullet can reach.
maximum height = ...........................................................[2]
The actual height reached by the bullet is less than the value calculated in (a)(ii).
(i) Explain, in terms of the forces acting on the bullet, why this is so.
[2]
(ii) As the bullet rises through the air, the amount of energy in its kinetic store decreases.
State what happens to this energy.
[2]
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Salmon are born in freshwater rivers, spend most of their lives in the sea, but return to freshwater rivers to breed. As they swim up rivers, they often have to jump up waterfalls.
Fig. 1.1 shows a salmon attempting to jump up a waterfall with a vertical height of 0.36 m.
Fig. 1.1
The salmon has a mass of 1.84 kg.
The salmon leaves the water with a speed of 3.2 m/s.
Determine whether the salmon can make the height required for the jump.
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Another salmon of mass 2.2 kg tries to make the jump.
Calculate the minimum speed with which the salmon would have to leave the water in order to reach the height required.
speed = ....................................
The salmon swim far upstream and encounter a high waterfall.
The salmon attempts to jump to the top of the waterfall, but fails, and performs a somersault during the decent. The salmon straightens out before it enters the water as shown in Fig. 1.2.
Discuss whether the speed of entry into the water is greater than, less than or equal to the speed with which it leaves the water. Ignore any effects of air resistance.
The temperature of the water at the bottom of a waterfall is greater than the temperature of the water at the top.
Suggest why this is the case.
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Define power.
A fairground amusement uses the arrangement shown in Fig. 1.1 to measure the individual power rating of customers.
Fig. 1.1
In the table below, list the quantities they must measure and the instrument used for measuring them.
| quantity to be measured | instrument used for measurement |
1. |
|
|
2. |
|
|
3. |
|
|
The mass of the load on the system is 30 kg. The length of rope able to pass through the pulley is 1.3 m.
The man pulled the rope as hard as he could and the time taken was measured to be 1.2 s.
(i) Determine the power rating of the man.
[3]
(ii) The amusement gave the man a power rating of 300 W.
Suggest a reason for the discrepancy.
[1]
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The man's body was only 19% efficient whilst pulling on the rope.
Calculate the total energy he used.
energy used = ....................................
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