O Level Physics Energy Power Quiz

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O-Level Physics Quiz - Energy Power

Name: ____________________
Class: ____________________
Date: ____________________
Score: ________ / 45

Duration: 60 minutes
Total Marks: 45

Instructions:

• Answer all questions in the spaces provided.
• Use $g = 10\text{ m/s}^2$ for all gravitational calculations.
• Show all working clearly for calculation questions.
• Give your answers to 2 or 3 significant figures.

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Section A: Conceptual Understanding (Questions 1–8)

1. State the principle of conservation of energy. [1]
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2. A ball is dropped from a height. Describe the energy transformation that occurs from the moment it is released until it hits the ground. [2]
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3. Define 'Power' in terms of energy transfer. [1]
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4. A machine has an efficiency of 40%. If the total energy input is 500 J, calculate the useful energy output. [2]
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5. Explain why the efficiency of a real-world motor is always less than 100%. [2]
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6. Distinguish between renewable and non-renewable energy resources. [2]
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7. A student claims that "work is done" when a person holds a heavy suitcase still for 5 minutes. Explain why this claim is physically incorrect. [2]
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8. Which energy store is primarily increased when a spring is compressed? [1]
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Section B: Calculations and Applications (Questions 9–16)

9. A crane lifts a mass of 200 kg vertically through a height of 15 m. Calculate the gravitational potential energy gained by the mass. [2]
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10. A car of mass 1200 kg is travelling at a constant speed of 20 m/s. Calculate its kinetic energy. [2]
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11. A motor with a power rating of 2.5 kW lifts a 50 kg load. Calculate the maximum height the load can be lifted in 4 seconds, assuming 100% efficiency. [3]
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12. A light bulb is rated at 60 W. Calculate the energy consumed by the bulb if it is left on for 2 hours. Give your answer in Joules. [2]
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13. An object of mass 0.5 kg is launched vertically upwards with a velocity of 10 m/s. Calculate the maximum height reached by the object. [3]
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14. A pump is used to lift 100 kg of water per minute to a height of 10 m. Calculate the average power of the pump. [3]
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15. A toy car is pushed with a constant force of 5 N over a distance of 2.0 m. Calculate the work done by the force. [2]
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16. An electric heater has a power output of 1.2 kW. If it is used for 30 minutes, calculate the total electrical energy transferred. [2]
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Section C: Integrated Analysis (Questions 17–20)

17. A roller coaster car of mass 500 kg starts from rest at point A (height 20 m) and descends to point B (height 5 m). (a) Calculate the loss in gravitational potential energy from A to B. [2]
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    (b) Assuming no friction, calculate the velocity of the car at point B. [3]
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18. A hydroelectric dam uses falling water to turn a turbine. (a) State the energy sequence: [Water at top] $\rightarrow$ [Falling water] $\rightarrow$ [Turbine] $\rightarrow$ [Generator]. [2]
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    (b) If the total potential energy of the water is $1.0 \times 10^6\text{ J}$ and the electrical energy produced is $7.5 \times 10^5\text{ J}$, calculate the efficiency of the system. [2]
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19. A 2.0 kg block is pushed across a rough horizontal floor. A force of 15 N is applied, but the block moves at a constant velocity. (a) What is the value of the frictional force? [1]
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    (b) Calculate the work done against friction if the block moves 4.0 m. [2]
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20. A student uses a 100 W motor to lift a 2 kg book. The motor takes 2 seconds to lift the book 1.0 m. (a) Calculate the useful work done in lifting the book. [2]
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    (b) Calculate the efficiency of the motor for this specific task. [2] \

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Answer Key - O-Level Physics Quiz: Energy Power

1. Energy cannot be created or destroyed; it can only be transformed from one form to another. (1)
2. Gravitational potential energy $\rightarrow$ Kinetic energy. (2)
3. Power is the rate of energy transfer (or rate of doing work). (1)
4. $\text{Useful energy} = 0.40 \times 500 = 200\text{ J}$. (2)
5. Some energy is dissipated/wasted as heat due to friction in bearings or electrical resistance in windings. (2)
6. Renewable: Resources that are replenished at the same rate they are used (e.g., solar). Non-renewable: Resources that are finite and will run out (e.g., coal). (2)
7. Work is defined as force $\times$ distance in the direction of the force. Since there is no distance moved, no work is done. (2)
8. Elastic potential energy. (1)
9. $E_p = mgh = 200 \times 10 \times 15 = 30,000\text{ J}$ (or $3.0 \times 10^4\text{ J}$). (2)
10. $E_k = \frac{1}{2}mv^2 = 0.5 \times 1200 \times 20^2 = 240,000\text{ J}$ (or $2.4 \times 10^5\text{ J}$). (2)
11. $\text{Total Energy} = P \times t = 2500 \times 4 = 10,000\text{ J}$. $h = \frac{E}{mg} = \frac{10000}{50 \times 10} = 20\text{ m}$. (3)
12. $E = P \times t = 60 \times (2 \times 3600) = 432,000\text{ J}$. (2)
13. $\text{KE at bottom} = \text{GPE at top} \rightarrow \frac{1}{2}mv^2 = mgh$. $h = \frac{v^2}{2g} = \frac{10^2}{2 \times 10} = 5.0\text{ m}$. (3)
14. $m = 100\text{ kg}$, $h = 10\text{ m}$, $t = 60\text{ s}$. $\text{Work} = 100 \times 10 \times 10 = 10,000\text{ J}$. $P = \frac{10000}{60} = 166.67\text{ W} \approx 167\text{ W}$. (3)
15. $W = Fd = 5 \times 2.0 = 10\text{ J}$. (2)
16. $E = P \times t = 1200 \times (30 \times 60) = 2,160,000\text{ J}$ (or $2.16 \times 10^6\text{ J}$). (2)
17. (a) $\Delta E_p = mg(h_1 - h_2) = 500 \times 10 \times (20 - 5) = 75,000\text{ J}$. (2) (b) $\frac{1}{2}mv^2 = 75,000 \rightarrow v^2 = \frac{150000}{500} = 300 \rightarrow v = \sqrt{300} \approx 17.3\text{ m/s}$. (3)
18. (a) Gravitational PE $\rightarrow$ Kinetic Energy $\rightarrow$ Electrical Energy. (2) (b) $\text{Eff} = \frac{7.5 \times 10^5}{1.0 \times 10^6} \times 100\% = 75\%$. (2)
19. (a) $15\text{ N}$ (since velocity is constant, net force is zero). (1) (b) $W = Fd = 15 \times 4.0 = 60\text{ J}$. (2)
20. (a) $W = mgh = 2 \times 10 \times 1.0 = 20\text{ J}$. (2) (b) $\text{Energy input} = P \times t = 100 \times 2 = 200\text{ J}$. $\text{Eff} = \frac{20}{200} \times 100\% = 10\%$. (2)