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Secondary 3 Physics Energy Power Quiz

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Questions

Secondary 3 Physics Quiz - Energy Power

Name: __________________________
Class: __________________________
Date: __________________________
Score: ________ / 40

Duration: 45 minutes
Total Marks: 40

Instructions:

Answer all questions.
Write your answers in the spaces provided.
Show all working clearly. Marks may be awarded for correct working even if the final answer is incorrect.
Take the acceleration due to gravity, $g = 10 \text{ m/s}^2$ .

Section A: Multiple Choice Questions (Questions 1–5)

Each question carries 1 mark.

1. Which of the following is a unit of power? A. Joule (J) B. Newton (N) C. Watt (W) D. Pascal (Pa)

Answer: _________

2. A ball is dropped from a height. As it falls, air resistance is negligible. Which energy transformation takes place? A. Kinetic energy to gravitational potential energy B. Gravitational potential energy to kinetic energy C. Chemical energy to kinetic energy D. Elastic potential energy to gravitational potential energy

Answer: _________

3. A machine lifts a load of 500 N through a vertical height of 2 m in 4 seconds. What is the useful power output of the machine? A. 250 W B. 500 W C. 1000 W D. 4000 W

Answer: _________

4. Which of the following statements about energy is correct? A. Energy can be created but not destroyed. B. Energy can be destroyed but not created. C. Energy can be both created and destroyed. D. Energy cannot be created or destroyed, only transferred or transformed.

Answer: _________

5. An electric motor has an efficiency of 80%. If the total electrical energy input is 1000 J, how much energy is wasted? A. 200 J B. 800 J C. 1000 J D. 1250 J

Answer: _________

Section B: Structured Questions (Questions 6–15)

Questions carry marks as indicated.

6. Define power.

[1]

7. State the Principle of Conservation of Energy.

[1]

8. A crane lifts a concrete block of mass 200 kg vertically upwards at a constant speed. The block rises by 15 m. (a) Calculate the gain in gravitational potential energy (GPE) of the block.

Answer space

Answer: ____________________ J [2]

(b) State the useful energy transfer that occurs during this lift.

[1]

9. A car of mass 1000 kg is traveling at a speed of 20 m/s. (a) Calculate the kinetic energy (KE) of the car.

Answer space

Answer: ____________________ J [2]

(b) The driver applies the brakes, and the car comes to a stop. Describe the main energy transformation that occurs during braking.

[1]

10. An electric heater has a power rating of 2 kW. It is switched on for 30 minutes. (a) Convert the power rating into Watts. Answer: ____________________ W [1]

(b) Convert the time into seconds. Answer: ____________________ s [1]

Answer space

Answer: ____________________ J [2]

11. A student pushes a box across a horizontal floor with a constant force of 50 N. The box moves a distance of 4 m in the direction of the force. (a) Calculate the work done by the student.

Answer space

Answer: ____________________ J [2]

(b) If the box moves at a constant speed, explain why the kinetic energy of the box does not change.

[1]

12. The diagram below shows a pendulum bob swinging from position A (highest point) to position B (lowest point).

Image pending generation for this question.

  A
 / \
/   \

O O

B

(a) At which position (A or B) is the gravitational potential energy maximum? Answer: ____________________ [1]

(b) At which position (A or B) is the kinetic energy maximum? Answer: ____________________ [1]

13. A pump raises 50 kg of water from a well to a tank 10 m above in 5 seconds. (a) Calculate the weight of the water.

Answer space

Answer: ____________________ N [1]

(b) Calculate the useful power output of the pump.

Answer space

Answer: ____________________ W [2]

14. A light bulb is rated at 60 W. It is replaced by an LED bulb rated at 10 W that provides the same brightness. (a) Calculate the energy saved per second by using the LED bulb.

Answer space

Answer: ____________________ J [1]

(b) Explain why the LED bulb is considered more efficient than the filament bulb.

[1]

15. A roller coaster car starts from rest at the top of a hill (Height = 30 m). It travels down the track to the bottom. Assume friction and air resistance are negligible. (a) State the relationship between the loss in GPE and the gain in KE.

[1]

(b) Calculate the speed of the car at the bottom of the hill.

Answer space

Answer: ____________________ m/s [3]

Section C: Free Response Questions (Questions 16–20)

Questions carry marks as indicated.

16. A construction worker uses a pulley system to lift a brick. The worker pulls the rope with a force of 60 N through a distance of 2 m. The brick (weight 100 N) rises by 1 m. (a) Calculate the work done by the worker (input work).

Answer space

Answer: ____________________ J [2]

(b) Calculate the useful work done on the brick (output work).

Answer space

Answer: ____________________ J [2]

Answer space

Answer: ____________________ % [2]

17. An electric kettle contains 1.5 kg of water at 20 °C. The kettle has a power rating of 2400 W. The specific heat capacity of water is 4200 J/(kg °C). (a) Calculate the energy required to raise the temperature of the water to 100 °C.

Answer space

Answer: ____________________ J [3]

(b) Calculate the minimum time taken to heat the water to 100 °C, assuming no energy is lost to the surroundings.

Answer space

Answer: ____________________ s [2]

18. A cyclist travels up a hill. The total mass of the cyclist and bicycle is 80 kg. The vertical height of the hill is 5 m. (a) Calculate the gain in gravitational potential energy.

Answer space

Answer: ____________________ J [2]

(b) In reality, the cyclist does more work than the value calculated in (a). Give two reasons for this difference.

[2]

19. A toy car of mass 0.5 kg is released from rest at the top of a ramp. At the bottom of the ramp, its speed is 2 m/s. The vertical height of the ramp is 0.3 m. (a) Calculate the GPE lost by the car.

Answer space

Answer: ____________________ J [2]

(b) Calculate the KE gained by the car.

Answer space

Answer: ____________________ J [2]

[1]

20. Two cranes, Crane A and Crane B, are used to lift identical loads to the same height. Crane A takes 10 seconds to complete the lift. Crane B takes 20 seconds to complete the lift. (a) Compare the work done by Crane A and Crane B.

[1]

(b) Compare the power developed by Crane A and Crane B. Explain your answer.

[2]

(c) If Crane A has an efficiency of 90% and Crane B has an efficiency of 80%, which crane wastes more energy as heat and sound? Explain.

[2]

End of Quiz

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Answers

Secondary 3 Physics Quiz - Energy Power (Answer Key)

Total Marks: 40

Section A: Multiple Choice Answers

1. C
Explanation: The SI unit of power is the Watt (W). Joule is energy, Newton is force, Pascal is pressure.

2. B
Explanation: As the ball falls, height decreases (loss of GPE) and speed increases (gain in KE).

3. A
Explanation: Work done = Force × distance = $500 \times 2 = 1000$ J. Power = Work / time = $1000 / 4 = 250$ W.

4. D
Explanation: This is the standard statement of the Principle of Conservation of Energy.

5. A
Explanation: Useful energy = $80\% \text{ of } 1000 = 800$ J. Wasted energy = Total Input - Useful Output = $1000 - 800 = 200$ J.

Section B: Structured Answers

6. Power is defined as the rate of doing work (or rate of energy transfer).
[1]

7. Energy cannot be created or destroyed; it can only be transformed from one form to another or transferred from one object to another.
[1]

8.
(a) $GPE = mgh$
$GPE = 200 \times 10 \times 15$
$GPE = 30,000$ J
[2] (1 mark for formula/substitution, 1 mark for answer)

(b) Electrical energy (from crane motor) to gravitational potential energy.
[1]

9.
(a) $KE = \frac{1}{2}mv^2$
$KE = 0.5 \times 1000 \times (20)^2$
$KE = 500 \times 400$
$KE = 200,000$ J
[2] (1 mark for formula/substitution, 1 mark for answer)

(b) Kinetic energy is transformed into thermal energy (heat) and sound energy due to friction in the brakes.
[1]

10.
(a) $2 \text{ kW} = 2000$ W
[1]

(b) $30 \text{ minutes} = 30 \times 60 = 1800$ s
[1]

(c) $E = P \times t$
$E = 2000 \times 1800$
$E = 3,600,000$ J (or $3.6 \times 10^6$ J)
[2] (1 mark for substitution, 1 mark for answer)

11.
(a) $W = F \times d$
$W = 50 \times 4$
$W = 200$ J
[2]

(b) Since the speed is constant, the kinetic energy ( $\frac{1}{2}mv^2$ ) remains constant. The work done by the student is used to overcome friction, not to increase speed.
[1]

12.
(a) A
[1]

(b) B
[1]

13.
(a) Weight $W = mg = 50 \times 10 = 500$ N
[1]

(b) Work done = $W \times h = 500 \times 10 = 5000$ J
Power $P = E / t = 5000 / 5 = 1000$ W
[2] (1 mark for work done, 1 mark for power)

14.
(a) Energy saved per second = Power difference = $60 - 10 = 50$ J
[1]

(b) The LED bulb converts a larger percentage of electrical energy into light energy and less into wasted heat energy compared to the filament bulb.
[1]

15.
(a) Loss in GPE = Gain in KE
[1]

(b) $mgh = \frac{1}{2}mv^2$
Mass cancels out: $gh = \frac{1}{2}v^2$
$10 \times 30 = 0.5 \times v^2$
$300 = 0.5 v^2$
$v^2 = 600$
$v = \sqrt{600} \approx 24.5$ m/s
[3] (1 mark for equation, 1 mark for substitution, 1 mark for answer)

Section C: Free Response Answers

16.
(a) Input Work = Force applied × distance moved by force
$W_{in} = 60 \times 2 = 120$ J
[2]

(b) Output Work = Load lifted × height lifted
$W_{out} = 100 \times 1 = 100$ J
[2]

(c) Efficiency = $\frac{\text{Useful Output Energy}}{\text{Total Input Energy}} \times 100\%$
Efficiency = $\frac{100}{120} \times 100\%$
Efficiency = $83.3\%$
[2] (1 mark for formula/sub, 1 mark for answer)

17.
(a) $\Delta T = 100 - 20 = 80$ °C
$Q = mc\Delta T$
$Q = 1.5 \times 4200 \times 80$
$Q = 504,000$ J
[3] (1 mark for $\Delta T$ , 1 mark for formula/sub, 1 mark for answer)

(b) $E = P \times t \Rightarrow t = E / P$
$t = 504,000 / 2400$
$t = 210$ s
[2] (1 mark for rearrangement/sub, 1 mark for answer)

18.
(a) $GPE = mgh = 80 \times 10 \times 5 = 4000$ J
[2]

(b) Any two of:

Work is done against air resistance.
Work is done against friction in the bicycle chain/wheels.
The cyclist also gains some kinetic energy if they are speeding up.
[2]

19.
(a) $GPE_{lost} = mgh = 0.5 \times 10 \times 0.3 = 1.5$ J
[2]

(b) $KE_{gained} = \frac{1}{2}mv^2 = 0.5 \times 0.5 \times (2)^2 = 0.5 \times 0.5 \times 4 = 1.0$ J
[2]

(c) Some energy is lost/converted to heat and sound due to friction between the wheels and the ramp/axle, and air resistance.
[1]

20.
(a) The work done is the same for both cranes because they lift identical loads (same force/weight) through the same vertical height (same distance). $W = Fd$ .
[1]

(b) Crane A develops greater power.
Power is the rate of doing work ( $P = W/t$ ). Since the work done is the same, the crane that takes less time (Crane A) has a higher power output.
[2] (1 mark for comparison, 1 mark for explanation)

(c) Crane B wastes more energy.
Efficiency = Useful Output / Total Input.
Lower efficiency means a larger proportion of the input energy is wasted. Since Crane B (80%) is less efficient than Crane A (90%), it wastes 20% of its input energy compared to Crane A's 10%. Assuming the useful work is the same, Crane B requires more total input energy, and thus wastes more absolute energy.
[2] (1 mark for identification, 1 mark for reasoning)