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Secondary 3 Physics Energy Power Quiz

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Questions

Secondary 3 Physics Quiz - Energy Power

Name: ________________________
Class: Secondary 3 ___
Date: ________________________
Score: ______ / 40

Duration: 45 minutes
Total Marks: 40

Instructions:

This quiz contains 20 questions on the topic of Energy and Power.
Answer ALL questions in the spaces provided.
Show all working clearly for calculation questions.
Take g = 10 N/kg unless otherwise stated.
Marks are indicated in brackets.

Section A: Multiple Choice (10 marks)

Circle the correct answer for each question.

1. Which of the following is the correct SI unit for power?

A. Joule (J)
B. Watt (W)
C. Newton (N)
D. Pascal (Pa)

[1 mark]

2. A machine does 600 J of useful work but requires 800 J of input energy. What is its efficiency?

A. 25%
B. 60%
C. 75%
D. 133%

[1 mark]

3. A student of mass 50 kg climbs a flight of stairs of vertical height 4 m in 5 seconds. What is the average power output?

A. 40 W
B. 200 W
C. 400 W
D. 2000 W

[1 mark]

4. Which energy transformation occurs when a moving car applies its brakes and comes to a stop?

A. Kinetic energy → Gravitational potential energy
B. Kinetic energy → Thermal energy
C. Chemical energy → Kinetic energy
D. Thermal energy → Kinetic energy

[1 mark]

5. Two objects, X and Y, have the same mass. Object X moves at 4 m/s and Object Y moves at 8 m/s. How does the kinetic energy of Y compare to that of X?

A. Y has twice the kinetic energy of X
B. Y has four times the kinetic energy of X
C. Y has the same kinetic energy as X
D. Y has eight times the kinetic energy of X

[1 mark]

6. A crane lifts a 200 kg load vertically upward at a constant speed of 0.5 m/s. What is the power developed by the crane?

A. 100 W
B. 500 W
C. 1000 W
D. 2000 W

[1 mark]

7. Which of the following is a non-renewable energy resource?

A. Solar energy
B. Wind energy
C. Natural gas
D. Hydroelectric energy

[1 mark]

8. A ball is thrown vertically upward. At its highest point, which statement is correct?

A. Kinetic energy is maximum, potential energy is minimum
B. Kinetic energy is minimum, potential energy is maximum
C. Both kinetic and potential energy are maximum
D. Both kinetic and potential energy are minimum

[1 mark]

9. An electric motor has a power rating of 1500 W. How much energy does it consume in 2 minutes?

A. 750 J
B. 3000 J
C. 90,000 J
D. 180,000 J

[1 mark]

10. A force of 50 N pushes a box 3 m along a horizontal floor. The frictional force opposing the motion is 20 N. What is the net work done on the box?

A. 60 J
B. 90 J
C. 150 J
D. 210 J

[1 mark]

Section B: Short Answer (10 marks)

Answer each question in the space provided.

11. State the principle of conservation of energy.

[1 mark]

12. A lamp converts 100 J of electrical energy into 15 J of light energy and 85 J of thermal energy. Calculate the efficiency of the lamp.

[2 marks]

13. Explain why a stretched rubber band possesses elastic potential energy.

[1 mark]

14. A student says, "A more powerful machine always does more work." Explain why this statement is incorrect.

[2 marks]

15. A cyclist travels at a constant speed along a flat road. The total resistive force acting on the cyclist and bicycle is 40 N. The cyclist covers 500 m in 50 seconds.

(a) Calculate the work done by the cyclist against the resistive forces. [2 marks]

(b) Calculate the power output of the cyclist. [2 marks]

Section C: Structured Questions (20 marks)

Answer all parts of each question. Show all working clearly.

16. A construction worker uses a pulley system to lift a bag of cement of mass 25 kg from the ground to a platform 8 m above the ground.

(a) Calculate the gain in gravitational potential energy of the bag of cement. [2 marks]

(b) The pulley system has an efficiency of 80%. Calculate the actual work input required to lift the bag. [2 marks]

17. A roller coaster car of mass 500 kg starts from rest at point A, which is 30 m above the ground. It travels down a frictionless track to point B at ground level, then rises to point C, which is 10 m above the ground.

(a) Calculate the gravitational potential energy of the car at point A. [2 marks]

(b) Using the principle of conservation of energy, calculate the speed of the car at point B. [3 marks]

(d) In reality, the track is not frictionless. Explain how this would affect the speed of the car at point C compared to your calculated value. [2 marks]

18. A household electric kettle has a power rating of 2200 W. It is used to heat 1.5 kg of water from 25 °C to 100 °C. The specific heat capacity of water is 4200 J/(kg °C).

(a) Calculate the amount of thermal energy required to heat the water. [2 marks]

(b) Assuming no energy losses, calculate the minimum time required for the kettle to heat the water. [2 marks]

(c) In practice, the kettle takes longer than the calculated time. Suggest one reason for this and explain how it affects the efficiency of the kettle. [1 mark]

19. A student investigates the power output of a small electric motor by using it to lift a mass of 0.5 kg through a vertical height of 1.2 m. The motor takes 3.0 seconds to lift the mass at constant speed.

(a) Calculate the work done by the motor in lifting the mass. [2 marks]

(b) Calculate the useful power output of the motor. [1 mark]

20. A car of mass 1200 kg accelerates from rest to a speed of 20 m/s along a horizontal road. The average driving force provided by the engine during this acceleration is 3000 N.

(a) Calculate the kinetic energy gained by the car. [2 marks]

(b) Calculate the work done by the engine if the car travels 100 m during the acceleration. [1 mark]

(c) The work done by the engine is greater than the kinetic energy gained by the car. Explain why this is the case and state what happens to the "missing" energy. [2 marks]

END OF QUIZ

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Answers

Secondary 3 Physics Quiz - Energy Power — Answer Key

Total Marks: 40

Section A: Multiple Choice (10 marks)

1. B. Watt (W)
The watt is the SI unit of power, defined as one joule per second.
[1 mark]

2. C. 75%
Efficiency = (useful output / total input) × 100% = (600 / 800) × 100% = 75%.
[1 mark]

3. C. 400 W
Work done = mgh = 50 × 10 × 4 = 2000 J. Power = work / time = 2000 / 5 = 400 W.
[1 mark]

4. B. Kinetic energy → Thermal energy
Braking converts the car's kinetic energy into thermal energy through friction between brake pads and discs.
[1 mark]

5. B. Y has four times the kinetic energy of X
KE ∝ v². Since v_Y = 2 × v_X, KE_Y = (2²) × KE_X = 4 × KE_X.
[1 mark]

6. C. 1000 W
Force needed = weight = mg = 200 × 10 = 2000 N. Power = force × velocity = 2000 × 0.5 = 1000 W.
[1 mark]

7. C. Natural gas
Natural gas is a fossil fuel and is non-renewable. Solar, wind, and hydroelectric are renewable resources.
[1 mark]

8. B. Kinetic energy is minimum, potential energy is maximum
At the highest point, velocity is zero (KE = 0, minimum) and height is maximum (GPE = maximum).
[1 mark]

9. D. 180,000 J
Energy = power × time = 1500 × (2 × 60) = 1500 × 120 = 180,000 J.
[1 mark]

10. B. 90 J
Net force = applied force − friction = 50 − 20 = 30 N. Net work = net force × distance = 30 × 3 = 90 J.
[1 mark]

Section B: Short Answer (10 marks)

11. Energy cannot be created or destroyed; it can only be transferred from one store to another or transformed from one form to another. The total energy of an isolated system remains constant.
Award [1] for a clear statement capturing conservation/transformation of energy.
[1 mark]

12. Efficiency = (useful energy output / total energy input) × 100%
Efficiency = (15 / 100) × 100% = 15%
Award [1] for correct formula/substitution, [1] for correct answer with unit.
[2 marks]

13. When a rubber band is stretched, work is done to deform it. This work is stored as elastic potential energy in the stretched molecular bonds. When released, this stored energy can be converted to kinetic energy.
Award [1] for linking work done to stored energy in deformation.
[1 mark]

14. Power is the rate of doing work (power = work / time). A more powerful machine does work at a faster rate, but the total work done also depends on how long the machine operates. A less powerful machine running for a longer time could do more total work than a powerful machine running briefly.
Award [1] for defining power as rate, [1] for explaining the role of time.
[2 marks]

15.
(a) Work done = force × distance = 40 × 500 = 20,000 J
Award [1] for correct formula, [1] for correct answer.
[2 marks]

(b) Power = work done / time = 20,000 / 50 = 400 W
Award [1] for correct formula, [1] for correct answer with unit.
[2 marks]

Section C: Structured Questions (20 marks)

16.
(a) GPE = mgh = 25 × 10 × 8 = 2000 J
Award [1] for correct formula, [1] for correct answer with unit.
[2 marks]

(b) Efficiency = (useful work output / work input) × 100%
80% = (2000 / work input) × 100%
Work input = 2000 / 0.80 = 2500 J
Award [1] for correct rearrangement, [1] for correct answer.
[2 marks]

(c) Input power = work input / time = 2500 / 4 = 625 W
Award [1] for correct formula, [1] for correct answer with unit.
[2 marks]

17.
(a) GPE at A = mgh = 500 × 10 × 30 = 150,000 J
Award [1] for correct formula, [1] for correct answer.
[2 marks]

(b) By conservation of energy: GPE at A = KE at B
150,000 = ½ × 500 × v²
v² = 150,000 / 250 = 600
v = √600 ≈ 24.5 m/s
Award [1] for stating conservation of energy, [1] for correct substitution, [1] for correct answer.
[3 marks]

(c) Energy at C = GPE at C + KE at C = mgh_C + ½mv²
150,000 = (500 × 10 × 10) + ½ × 500 × v²
150,000 = 50,000 + 250v²
250v² = 100,000
v² = 400
v = 20 m/s
Award [1] for correct energy equation, [1] for correct answer.
[2 marks]

(d) With friction, some mechanical energy would be converted to thermal energy due to work done against friction. The total mechanical energy at point C would be less than the initial GPE, so the speed at C would be lower than the calculated value.
Award [1] for identifying energy loss to friction, [1] for explaining effect on speed.
[2 marks]

18.
(a) Q = mcΔθ = 1.5 × 4200 × (100 − 25) = 1.5 × 4200 × 75 = 472,500 J
Award [1] for correct formula/substitution, [1] for correct answer.
[2 marks]

(b) Energy = power × time → time = energy / power
Time = 472,500 / 2200 ≈ 214.8 s (or 3 min 35 s)
Award [1] for correct formula, [1] for correct answer.
[2 marks]

(c) Heat is lost to the surroundings (or the kettle body absorbs some heat). This means more electrical energy is needed to heat the water, reducing the efficiency of the kettle.
Award [1] for a valid reason with brief explanation.
[1 mark]

19.
(a) Work done = force × distance = weight × height = (0.5 × 10) × 1.2 = 5 × 1.2 = 6.0 J
Award [1] for correct force calculation, [1] for correct work.
[2 marks]

(b) Useful power output = work done / time = 6.0 / 3.0 = 2.0 W
Award [1] for correct answer with unit.
[1 mark]

(c) Efficiency = (useful power output / rated power) × 100% = (2.0 / 3.0) × 100% ≈ 66.7%
Award [1] for correct formula, [1] for correct answer.
[2 marks]

20.
(a) KE = ½mv² = ½ × 1200 × 20² = 600 × 400 = 240,000 J
Award [1] for correct formula, [1] for correct answer.
[2 marks]

(b) Work done by engine = force × distance = 3000 × 100 = 300,000 J
Award [1] for correct answer.
[1 mark]

(c) The work done by the engine (300,000 J) is greater than the kinetic energy gained (240,000 J) because some energy is used to do work against friction and air resistance. This "missing" energy (60,000 J) is converted to thermal energy in the tyres, road, and surrounding air.
Award [1] for identifying friction/resistive forces, [1] for explaining energy dissipation as heat.
[2 marks]

END OF ANSWER KEY