Secondary 3 Physics Energy Power Quiz

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Secondary 3 Physics Quiz - Energy Power

Name: ____________________ Class: __________ Date: __________ Score: ________ / 50

Duration: 60 Minutes
Total Marks: 50
Instructions: Answer all questions. Show all working clearly for calculation questions. Use $g = 10\text{ m/s}^2$ unless otherwise stated.

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Section A: Multiple Choice (1-8)

Circle the most appropriate option. (1 mark each)

1. Which of the following is a scalar quantity? A) Velocity B) Displacement C) Kinetic Energy D) Force

2. An object of mass $2\text{ kg}$ is lifted vertically through a height of $5\text{ m}$. The gain in gravitational potential energy is: A) $10\text{ J}$ B) $50\text{ J}$ C) $100\text{ J}$ D) $200\text{ J}$

3. If the velocity of a moving car is doubled, its kinetic energy increases by a factor of: A) 2 B) 4 C) 8 D) 16

4. A force of $20\text{ N}$ moves a block $3\text{ m}$ in the direction of the force. The work done is: A) $6.67\text{ J}$ B) $17\text{ J}$ C) $60\text{ J}$ D) $120\text{ J}$

5. Power is defined as: A) The total energy stored in a system B) The rate of doing work C) The product of force and distance D) The capacity to do work

6. A machine is 60% efficient. If the total energy input is $500\text{ J}$, the useful energy output is: A) $300\text{ J}$ B) $400\text{ J}$ C) $833\text{ J}$ D) $1100\text{ J}$

7. Which energy store is primary in a stretched rubber band? A) Chemical potential energy B) Gravitational potential energy C) Elastic potential energy D) Internal energy

8. A $100\text{ W}$ bulb is switched on for 10 seconds. The electrical energy consumed is: A) $10\text{ J}$ B) $100\text{ J}$ C) $1000\text{ J}$ D) $10,000\text{ J}$

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Section B: Short Answer & Calculations (9-15)

Show all working. (Marks indicated)

9. State the Principle of Conservation of Energy. [2]
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10. A ball of mass $0.5\text{ kg}$ is thrown vertically upwards with an initial speed of $10\text{ m/s}$. Calculate its kinetic energy at the moment of release. [2]
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11. Using the ball from Question 10, calculate the maximum height it reaches, assuming no air resistance. [3]
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12. A crane lifts a $200\text{ kg}$ crate to a height of $15\text{ m}$ in $10\text{ seconds}$. Calculate the average power output of the crane. [3]
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13. A student pushes a heavy box across a rough floor with a constant force of $50\text{ N}$ over a distance of $4\text{ m}$. If the box gains no kinetic energy, explain what happens to the work done by the student. [2]
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14. An electric motor is used to lift a weight. The total electrical energy input is $2000\text{ J}$, and the gravitational potential energy gained by the weight is $1500\text{ J}$. Calculate the efficiency of the motor. [2]
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15. A car of mass $1200\text{ kg}$ accelerates from $10\text{ m/s}$ to $20\text{ m/s}$. Calculate the increase in its kinetic energy. [3]
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Section C: Structured Application (16-20)

Detailed responses required. (Marks indicated)

16. A roller coaster car of mass $500\text{ kg}$ starts from rest at the top of a hill (Point A) at a height of $40\text{ m}$. (a) Calculate the GPE of the car at Point A. [2]
    
    (b) If the car slides down to Point B (ground level) without friction, calculate its speed at Point B. [3]
    
    (c) In reality, the speed at Point B is found to be $25\text{ m/s}$. Explain this difference. [2]
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17. A pump is used to lift $100\text{ kg}$ of water every minute from a well $10\text{ m}$ deep. (a) Calculate the work done by the pump in one minute. [2]
    
    (b) Calculate the power of the pump in Watts. [2]
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18. Compare and contrast "Work Done" and "Power". Use a real-world example to illustrate the difference. [4]
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19. A $60\text{ kg}$ climber climbs a vertical wall of $10\text{ m}$ in $2\text{ minutes}$. (a) Calculate the work done against gravity. [2]
    
    (b) Calculate the power developed by the climber. [2]
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20. A toy car is powered by a spring. When the spring is compressed, it stores $5\text{ J}$ of elastic potential energy. When released, the car moves $2\text{ m}$ across a floor. If $2\text{ J}$ of energy is lost to friction, calculate the final kinetic energy of the car. [4]
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Answer Key - Secondary 3 Physics Quiz: Energy Power

Section A: Multiple Choice

1. C (Kinetic Energy - Energy is a scalar)
2. C ($GPE = mgh = 2 \times 10 \times 5 = 100\text{ J}$)
3. B ($KE \propto v^2$; $2^2 = 4$)
4. C ($W = Fd = 20 \times 3 = 60\text{ J}$)
5. B (Rate of doing work)
6. A ($0.6 \times 500 = 300\text{ J}$)
7. C (Elastic potential energy)
8. C ($E = Pt = 100 \times 10 = 1000\text{ J}$)

Section B: Short Answer & Calculations

9. Energy cannot be created or destroyed, only transformed from one form to another. (Total energy of an isolated system remains constant). [2]
10. $KE = \frac{1}{2}mv^2 = 0.5 \times 0.5 \times 10^2 = 0.25 \times 100 = 25\text{ J}$. [2]
11. $KE_{\text{bottom}} = GPE_{\text{top}} \implies 25 = 0.5 \times 10 \times h \implies 25 = 5h \implies h = 5\text{ m}$. [3]
12. $W = mgh = 200 \times 10 \times 15 = 30,000\text{ J}$. $P = W/t = 30,000 / 10 = 3,000\text{ W}$ (or $3\text{ kW}$). [3]
13. The work done is converted into internal energy (heat) of the box and the floor due to friction. [2]
14. $\text{Efficiency} = (\text{Useful Output} / \text{Total Input}) \times 100 = (1500 / 2000) \times 100 = 75\%$. [2]
15. $\Delta KE = \frac{1}{2}m(v_f^2 - v_i^2) = 0.5 \times 1200 \times (20^2 - 10^2) = 600 \times (400 - 100) = 600 \times 300 = 180,000\text{ J}$. [3]

Section C: Structured Application

16. (a) $GPE = 500 \times 10 \times 40 = 200,000\text{ J}$. [2] (b) $200,000 = \frac{1}{2} \times 500 \times v^2 \implies 200,000 = 250v^2 \implies v^2 = 800 \implies v = \sqrt{800} \approx 28.3\text{ m/s}$. [3] (c) Some GPE was converted into thermal energy (heat) and sound energy due to friction and air resistance. [2]
17. (a) $W = mgh = 100 \times 10 \times 10 = 10,000\text{ J}$. [2] (b) $P = W/t = 10,000 / 60 \approx 166.7\text{ W}$. [2]
18. Work is the total energy transferred when a force moves an object ($W=Fd$). Power is the speed at which that energy is transferred ($P=W/t$). Example: Lifting a box slowly vs. lifting it quickly requires the same Work, but the latter requires more Power. [4]
19. (a) $W = 60 \times 10 \times 10 = 6,000\text{ J}$. [2] (b) $t = 120\text{ s}$. $P = 6,000 / 120 = 50\text{ W}$. [2]
20. $\text{Total Energy} = \text{KE} + \text{Energy lost to friction}$. $5\text{ J} = \text{KE} + 2\text{ J} \implies \text{KE} = 3\text{ J}$. [4]