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Secondary 3 Physics Energy Power Quiz

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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 statements correctly describes the principle of conservation of energy? A. Energy can be created but not destroyed. B. Energy can be destroyed but not created. C. The total energy of an isolated system remains constant. D. Kinetic energy is always converted into potential energy.

Answer: _______________ [1]

2. A crane lifts a load of mass 500 kg vertically through a height of 20 m in 10 seconds. What is the useful power output of the crane? A. 1,000 W B. 10,000 W C. 100,000 W D. 1,000,000 W

Answer: _______________ [1]

3. A ball is dropped from a height. As it falls, air resistance acts on it. Which of the following energy changes occurs? A. Gravitational potential energy $\rightarrow$ Kinetic energy only. B. Gravitational potential energy $\rightarrow$ Kinetic energy + Thermal energy. C. Kinetic energy $\rightarrow$ Gravitational potential energy. D. Chemical energy $\rightarrow$ Kinetic energy.

Answer: _______________ [1]

4. An electric motor has an efficiency of 80%. If the total energy input to the motor is 500 J, how much energy is wasted? A. 100 J B. 400 J C. 500 J D. 625 J

Answer: _______________ [1]

5. Two students, A and B, climb up the same flight of stairs. Student A takes 10 seconds, and Student B takes 15 seconds. They have the same mass. Which statement is correct? A. Student A does more work than Student B. B. Student B does more work than Student A. C. Student A develops more power than Student B. D. Student B develops more power than Student A.

Answer: _______________ [1]

Section B: Structured Questions (Questions 6–15)

6. Define the term power.

_________________________________________________________________________ [1]

7. A car of mass 1,200 kg is traveling at a speed of 20 m/s. (a) Calculate the kinetic energy of the car. <br> <br> <br> Kinetic Energy = ____________________ J [2]

(b) The car brakes and comes to a stop. State the main energy transformation that takes place. _________________________________________________________________________ [1]

8. A worker pushes a box with a constant horizontal force of 50 N across a floor for a distance of 8 m. (a) Calculate the work done by the worker. <br> <br> <br> Work Done = ____________________ J [2]

(b) If the worker takes 4 seconds to push the box, calculate the power developed by the worker. <br> <br> <br> Power = ____________________ W [2]

9. A hydroelectric power station uses water falling from a height of 150 m to generate electricity. (a) Calculate the loss in gravitational potential energy of 1 kg of water falling through this height. <br> <br> <br> Loss in GPE = ____________________ J [2]

(b) State one reason why the electrical energy generated is less than the loss in gravitational potential energy calculated in (a).

_________________________________________________________________________ [1]

10. An electric heater is rated at 2 kW. It is switched on for 30 minutes. (a) Convert the power rating into Watts. Power = ____________________ W [1]

(b) Calculate the total energy supplied by the heater in Joules. <br> <br> <br> Energy = ____________________ J [2]

11. A pendulum bob is pulled to one side and released. It swings back and forth. (a) At which point in its swing does the bob have maximum kinetic energy? _________________________________________________________________________ [1]

(b) Explain why the pendulum eventually stops swinging.

_________________________________________________________________________ [2]

12. A machine lifts a load of 800 N through a vertical height of 5 m. The total energy input to the machine is 5,000 J. (a) Calculate the useful work output. <br> <br> <br> Useful Work Output = ____________________ J [2]

(b) Calculate the efficiency of the machine. <br> <br> <br> Efficiency = ____________________ % [2]

13. A cyclist travels at a constant speed on a level road. (a) State the relationship between the driving force and the resistive forces (friction and air resistance). _________________________________________________________________________ [1]

(b) If the cyclist increases their speed, what happens to the air resistance? _________________________________________________________________________ [1]

14. A spring is stretched by a force. (a) Name the type of potential energy stored in the stretched spring. _________________________________________________________________________ [1]

(b) State the condition required for the spring to return to its original length when the force is removed. _________________________________________________________________________ [1]

15. A student claims that "if an object is not moving, it has no energy." Is this statement correct? Explain your answer with an example.

_________________________________________________________________________ [2]

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

16. A roller coaster car of mass 600 kg starts from rest at the top of a hill (Point A) which is 40 m above the ground. It travels down to Point B, which is at ground level. Assume there is no friction or air resistance. (a) Calculate the gravitational potential energy of the car at Point A. <br> <br> <br> GPE = ____________________ J [2]

(b) State the kinetic energy of the car at Point B. <br> <br> KE = ____________________ J [1]

(c) Calculate the speed of the car at Point B. <br> <br> <br> Speed = ____________________ m/s [3]

17. An electric pump lifts water from a well. The pump raises 100 kg of water every minute through a vertical height of 12 m. (a) Calculate the weight of the water lifted every minute. <br> <br> Weight = ____________________ N [1]

(b) Calculate the work done in lifting this water every minute. <br> <br> <br> Work Done = ____________________ J [2]

(c) Calculate the minimum power output required from the pump. <br> <br> <br> Power = ____________________ W [2]

18. A car engine converts chemical energy from fuel into kinetic energy. (a) Explain why the efficiency of a car engine is always less than 100%.

_________________________________________________________________________ [2]

(b) Suggest two ways in which energy is wasted in a car engine.

______________________________________________________________________ [2]

19. A block of mass 5 kg slides down a rough inclined plane. The vertical height of the plane is 3 m. The block starts from rest and reaches the bottom with a speed of 4 m/s. (a) Calculate the loss in gravitational potential energy. <br> <br> <br> Loss in GPE = ____________________ J [2]

(b) Calculate the gain in kinetic energy. <br> <br> <br> Gain in KE = ____________________ J [2]

(c) Explain the difference between the values calculated in (a) and (b).

_________________________________________________________________________ [2]

20. Two light bulbs, Bulb X and Bulb Y, provide the same amount of light energy per second. Bulb X is an incandescent bulb rated at 60 W. Bulb Y is an LED bulb rated at 10 W. (a) Which bulb is more efficient? Explain your answer.

_________________________________________________________________________ [2]

(b) Calculate the energy saved by using Bulb Y instead of Bulb X if both are used for 5 hours. Give your answer in kilowatt-hours (kWh). <br> <br> <br> <br> Energy Saved = ____________________ kWh [3]

Answers

Secondary 3 Physics Quiz - Energy Power (Answer Key)

1. C
2. B
Working: $P = \frac{W}{t} = \frac{mgh}{t} = \frac{500 \times 10 \times 20}{10} = 10,000 \text{ W}$
3. B
4. A
Working: Useful energy = $0.80 \times 500 = 400 \text{ J}$ . Wasted = $500 - 400 = 100 \text{ J}$ .
5. C
Working: Work done is same ( $mgh$ ). Power $P = W/t$ . Smaller $t$ means larger $P$ .

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

7. (a) $KE = \frac{1}{2}mv^2 = \frac{1}{2} \times 1200 \times (20)^2 = 600 \times 400 = 240,000 \text{ J}$ [2]
(b) Kinetic energy is converted to thermal energy (and sound energy). [1]

8. (a) $W = F \times d = 50 \times 8 = 400 \text{ J}$ [2]
(b) $P = \frac{W}{t} = \frac{400}{4} = 100 \text{ W}$ [2]

9. (a) $\Delta GPE = mgh = 1 \times 10 \times 150 = 1,500 \text{ J}$ [2]
(b) Energy is lost due to friction in the turbines/pipes or converted to heat/sound. [1]

10. (a) $2 \text{ kW} = 2,000 \text{ W}$ [1]
(b) Time $t = 30 \times 60 = 1,800 \text{ s}$ .
$E = P \times t = 2,000 \times 1,800 = 3,600,000 \text{ J}$ [2]

11. (a) At the lowest point of the swing. [1]
(b) Energy is dissipated as thermal energy and sound due to air resistance and friction at the pivot. Eventually, all mechanical energy is lost. [2]

12. (a) Useful Work Output = Force $\times$ distance = $800 \times 5 = 4,000 \text{ J}$ [2]
(b) Efficiency = $\frac{\text{Useful Output}}{\text{Total Input}} \times 100\% = \frac{4000}{5000} \times 100\% = 80\%$ [2]

13. (a) The driving force is equal in magnitude to the resistive forces. [1]
(b) Air resistance increases. [1]

14. (a) Elastic potential energy. [1]
(b) The limit of proportionality (or elastic limit) has not been exceeded. [1]

15. No, the statement is incorrect. [1]
An object at rest at a height has gravitational potential energy. A compressed spring has elastic potential energy. [1]

16. (a) $GPE = mgh = 600 \times 10 \times 40 = 240,000 \text{ J}$ [2]
(b) By conservation of energy (no losses), $KE = GPE_{lost} = 240,000 \text{ J}$ [1]
(c) $KE = \frac{1}{2}mv^2 \Rightarrow 240,000 = \frac{1}{2} \times 600 \times v^2$
$240,000 = 300 v^2$
$v^2 = 800$
$v = \sqrt{800} \approx 28.3 \text{ m/s}$ [3]

17. (a) Weight $W = mg = 100 \times 10 = 1,000 \text{ N}$ [1]
(b) Work Done $= W \times h = 1,000 \times 12 = 12,000 \text{ J}$ [2]
(c) Time $t = 60 \text{ s}$ .
$P = \frac{W}{t} = \frac{12,000}{60} = 200 \text{ W}$ [2]

18. (a) Energy cannot be created or destroyed, but in any conversion, some energy is dissipated to the surroundings (usually as heat) due to friction and other inefficiencies, so useful output is always less than input. [2]
(b) 1. Heat loss to surroundings/exhaust gases. [1]
2. Sound energy / Friction in moving parts. [1]

19. (a) Loss in GPE $= mgh = 5 \times 10 \times 3 = 150 \text{ J}$ [2]
(b) Gain in KE $= \frac{1}{2}mv^2 = \frac{1}{2} \times 5 \times (4)^2 = 2.5 \times 16 = 40 \text{ J}$ [2]
(c) The difference ( $150 - 40 = 110 \text{ J}$ ) is energy lost/work done against friction between the block and the rough plane, converted to thermal energy. [2]

20. (a) Bulb Y (LED) is more efficient. [1]
It produces the same light output (useful energy) but consumes less total electrical energy (10 W vs 60 W), meaning less energy is wasted. [1]
(b) Power difference $= 60 \text{ W} - 10 \text{ W} = 50 \text{ W} = 0.05 \text{ kW}$ .
Time $= 5 \text{ hours}$ .
Energy Saved $= P \times t = 0.05 \text{ kW} \times 5 \text{ h} = 0.25 \text{ kWh}$ . [3]