Secondary 4 Pure Physics Energy Power Quiz

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Secondary 4 Pure Physics Quiz - Energy Power

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

Duration: 60 Minutes
Total Marks: 45 Marks

Instructions:

• Answer all questions.
• For calculations, show all working clearly.
• Use $g = 10\text{ m/s}^2$ where necessary.
• Express final answers to 2 or 3 significant figures.

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Section A: Conceptual Foundations (Questions 1–5)

1. State the Principle of Conservation of Energy. [2]
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2. Distinguish between a renewable and a non-renewable energy resource, providing one example for each. [2]
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3. A ball is dropped from a height $h$. Describe the energy transformations that occur from the moment it is released until it hits the ground (ignore air resistance). [2]
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4. Define "Work Done" in physics and state its SI unit. [2]
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5. Explain why the efficiency of a real-world machine can never be 100%. [2]
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Section B: Quantitative Applications (Questions 6–15)

6. A bullet of mass 15 g is fired at a speed of 400 m/s. Calculate the kinetic energy of the bullet. [2]
   
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7. A crane lifts a load of 200 kg to a height of 12 m in 15 seconds. Calculate the useful work done by the crane. [2]
   
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8. Based on the answer in Question 7, calculate the useful power output of the crane. [2]
   
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9. A motor has an efficiency of 75%. If the electrical power input is 1200 W, determine the useful power output. [2]
   
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10. A 0.5 kg block is pushed across a rough horizontal floor by a constant force of 20 N over a distance of 4.0 m. Calculate the work done by the force. [2]
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11. A diver of mass 60 kg jumps from a platform 10 m high. Calculate the gravitational potential energy at the start. [2]
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12. Using the conservation of energy, calculate the speed of the diver just before hitting the water (ignore air resistance). [3]
    
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13. An electric kettle is rated at 2.5 kW. Calculate the energy transferred to the water if the kettle is switched on for 3 minutes. [3]
    
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14. A mass of 2.0 kg is accelerated from rest to a speed of 8.0 m/s. Calculate the increase in its kinetic energy. [2]
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15. A machine requires 5000 J of energy to perform a task, but 1500 J is dissipated as heat. Calculate the efficiency of the machine. [3]
    
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Section C: Integrated Problems (Questions 16–20)

16. A car of mass 1200 kg accelerates from 10 m/s to 20 m/s. Calculate the additional energy required for this acceleration. [3]
    
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17. A pump is used to lift 50 kg of water per minute from a well 10 m deep. Calculate the minimum power required by the pump. [3]
    
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18. An electric motor with an efficiency of 80% is used to lift a mass of 10 kg at a constant speed of 0.4 m/s. Calculate the electrical power input. [4]
    
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19. A 0.2 kg ball is thrown vertically upwards with a speed of 15 m/s. Calculate the maximum height reached by the ball. [4]
    
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20. A heater is used to heat 0.5 kg of water from 25°C to 85°C. If the heater has a power of 1000 W, calculate the time taken for this process. (Specific heat capacity of water = 4200 J/kg·K). [4]
    
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Answer Key - Secondary 4 Pure Physics Quiz: Energy Power

1. Principle of Conservation of Energy

• Energy cannot be created or destroyed, only converted from one form to another. [1]
• The total energy in an isolated system remains constant. [1]

2. Renewable vs Non-renewable

• Renewable: Energy from sources that are replenished naturally over short periods (e.g., solar, wind). [1]
• Non-renewable: Energy from sources that are depleted over time and cannot be replaced quickly (e.g., coal, oil, natural gas). [1]

3. Energy Transformations

• Gravitational Potential Energy (GPE) $\rightarrow$ Kinetic Energy (KE). [2]

4. Work Done

• Definition: The product of the force applied to an object and the distance moved in the direction of the force. [1]
• Unit: Joule (J). [1]

5. Efficiency

• Energy is always dissipated to the surroundings, usually as heat/sound due to friction or air resistance. [2]

6. Kinetic Energy

• $m = 0.015\text{ kg}$, $v = 400\text{ m/s}$
• $KE = \frac{1}{2} \times 0.015 \times 400^2 = 1200\text{ J}$ [2]

7. Useful Work Done

• $W = mgh = 200 \times 10 \times 12 = 24,000\text{ J}$ [2]

8. Useful Power Output

• $P = W/t = 24,000 / 15 = 1600\text{ W}$ [2]

9. Useful Power Output

• $P_{out} = 0.75 \times 1200 = 900\text{ W}$ [2]

10. Work Done

• $W = F \times d = 20 \times 4.0 = 80\text{ J}$ [2]

11. GPE

• $GPE = mgh = 60 \times 10 \times 10 = 6000\text{ J}$ [2]

12. Speed of Diver

• $GPE_{top} = KE_{bottom}$
• $6000 = \frac{1}{2} \times 60 \times v^2$
• $v^2 = 200 \rightarrow v = 14.1\text{ m/s}$ [3]

13. Energy Transferred

• $P = 2500\text{ W}$, $t = 180\text{ s}$
• $E = P \times t = 2500 \times 180 = 450,000\text{ J}$ (or $4.5 \times 10^5\text{ J}$) [3]

14. Increase in KE

• $\Delta KE = \frac{1}{2} \times 2.0 \times (8^2 - 0^2) = 64\text{ J}$ [2]

15. Efficiency

• Total input = $5000\text{ J}$, Useful output = $5000 - 1500 = 3500\text{ J}$
• $\text{Efficiency} = (3500 / 5000) \times 100\% = 70\%$ [3]

16. Additional Energy

• $\Delta KE = \frac{1}{2} \times 1200 \times (20^2 - 10^2)$
• $\Delta KE = 600 \times (400 - 100) = 180,000\text{ J}$ [3]

17. Minimum Power

• $m = 50\text{ kg}$, $h = 10\text{ m}$, $t = 60\text{ s}$
• $P = (50 \times 10 \times 10) / 60 = 5000 / 60 = 83.3\text{ W}$ [3]

18. Electrical Power Input

• $P_{out} = Fv = (10 \times 10) \times 0.4 = 40\text{ W}$ [2]
• $P_{in} = 40 / 0.8 = 50\text{ W}$ [2]

19. Maximum Height

• $KE_{bottom} = GPE_{top}$
• $\frac{1}{2} \times 0.2 \times 15^2 = 0.2 \times 10 \times h$
• $0.1 \times 225 = 2h \rightarrow 22.5 = 2h \rightarrow h = 11.25\text{ m}$ [4]

20. Time Taken

• $Q = mc\Delta\theta = 0.5 \times 4200 \times (85 - 25) = 2100 \times 60 = 126,000\text{ J}$ [2]
• $t = Q / P = 126,000 / 1000 = 126\text{ s}$ [2]