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Secondary 4 Pure Physics Energy Power Quiz

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Secondary 4 Pure Physics Quiz - Energy Power

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

Duration: 45 minutes
Total Marks: 45

Instructions:

Answer all questions.
Write your answers in the spaces provided.
Show all working clearly. Marks are 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 & Short Concepts (Questions 1–5)

[10 Marks]

1. Which of the following is a vector quantity?
A. Energy
B. Power
C. Work
D. Force

Answer: _______________ [1]

2. A student lifts a box of mass 5 kg vertically through a height of 2 m in 4 seconds. What is the average power developed by the student?
A. 2.5 W
B. 10 W
C. 25 W
D. 100 W

Answer: _______________ [1]

3. State the Principle of Conservation of Energy.

_________________________________________________________________________ [1]

4. A machine has an efficiency of 80%. If the total energy input is 500 J, calculate the useful energy output.

_________________________________________________________________________ [1]

5. Identify the primary energy conversion taking place in a hydroelectric power station when water flows from the reservoir through the turbines.
_________________________________________________________________________ [1]

Section B: Structured Calculations (Questions 6–12)

[21 Marks]

6. A crane lifts a load of mass 200 kg vertically at a constant speed. The load rises 15 m in 30 seconds.
(a) Calculate the gain in gravitational potential energy (GPE) of the load.
 
Answer: _______________ J [2]

(b) Calculate the power output of the crane motor.
 
Answer: _______________ W [2]

7. A car of mass 1200 kg is travelling at a speed of 20 m/s.
(a) Calculate the kinetic energy (KE) of the car.
 
Answer: _______________ J [2]

(b) The driver applies the brakes, and the car comes to a stop over a distance of 40 m. Calculate the average braking force exerted on the car.
 
Answer: _______________ N [2]

8. An electric motor lifts a 50 N weight through a vertical height of 3 m. The motor consumes 200 J of electrical energy.
(a) Calculate the useful work done on the weight.
 
Answer: _______________ J [1]

(b) Calculate the efficiency of the motor.
 
Answer: _______________ % [2]

9. A pendulum bob of mass 0.2 kg is released from rest at point A, which is 0.5 m higher than its lowest point B.
(a) Calculate the loss in GPE as the bob moves from A to B.
 
Answer: _______________ J [1]

(b) Assuming air resistance is negligible, calculate the speed of the bob at point B.
 
Answer: _______________ m/s [2]

10. A pump raises 100 kg of water from a well 10 m deep in 20 seconds.
(a) Calculate the work done against gravity.
 
Answer: _______________ J [1]

(b) If the pump motor has a power rating of 1000 W, calculate the efficiency of the pump system.
 
Answer: _______________ % [2]

11. A cyclist travels up a hill. The total mass of the cyclist and bicycle is 80 kg. The vertical height of the hill is 10 m.
(a) Calculate the minimum work done by the cyclist to reach the top.
 
Answer: _______________ J [1]

(b) In reality, the cyclist does 10,000 J of work. Explain why this value is higher than your answer in (a).

_________________________________________________________________________ [1]

12. Define power in terms of energy and time.
_________________________________________________________________________ [1]

Section C: Application & Analysis (Questions 13–20)

[14 Marks]

13. A roller coaster car starts from rest at the top of a hill (Point X) and travels down to the bottom (Point Y).
(a) Describe the energy changes as the car moves from X to Y.
 
_________________________________________________________________________ [1]

(b) At Point Y, the car has a speed of 25 m/s. Calculate the vertical height of Point X above Point Y, assuming no energy losses.
 
Answer: _______________ m [2]

14. An electric kettle is rated at 240 V, 2000 W. It takes 3 minutes to boil a certain amount of water.
(a) Calculate the total electrical energy supplied to the kettle.
 
Answer: _______________ J [2]

(b) The water absorbs 300,000 J of thermal energy. Calculate the energy wasted.
 
Answer: _______________ J [1]

15. Explain why the efficiency of any machine is always less than 100%.

_________________________________________________________________________ [1]

16. A student claims that "a more powerful machine always does more work than a less powerful machine." Is this statement correct? Explain your answer.

_________________________________________________________________________ [2]

17. A box is pushed horizontally across a rough floor with a constant force of 50 N for a distance of 10 m.
(a) Calculate the work done by the pushing force.
 
Answer: _______________ J [1]

(b) If the box moves at a constant speed, what happens to the work done by the pushing force?
 
_________________________________________________________________________ [1]

18. Solar panels are used to generate electricity.
(a) State the energy conversion in a solar panel.
 
_________________________________________________________________________ [1]

(b) Suggest one advantage and one disadvantage of using solar energy compared to fossil fuels.
 
Advantage: ______________________________________________________________
Disadvantage: ___________________________________________________________ [2]

19. A ball is dropped from a height. It bounces back up but does not reach the original height.
Explain, in terms of energy, why the ball does not return to the original height.

_________________________________________________________________________ [1]

20. A factory uses a motor to lift crates. The motor is rated at 5 kW. It lifts a crate of mass 500 kg through a height of 20 m in 25 seconds.
Calculate the efficiency of the motor.
 
Answer: _______________ % [3]

Answers

Secondary 4 Pure Physics Quiz - Energy Power (Answer Key)

1. D
Explanation: Force has both magnitude and direction. Energy, Power, and Work are scalar quantities. [1]

2. C
Explanation:
Work Done = $mgh = 5 \times 10 \times 2 = 100 \text{ J}$ .
Power = $\text{Work} / \text{time} = 100 / 4 = 25 \text{ W}$ . [1]

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

4. 400 J
Explanation:
$\text{Efficiency} = (\text{Useful Output} / \text{Total Input}) \times 100\%$
$80 = (\text{Output} / 500) \times 100$
$\text{Output} = 0.8 \times 500 = 400 \text{ J}$ . [1]

5. Gravitational Potential Energy $\rightarrow$ Kinetic Energy $\rightarrow$ Electrical Energy.
(Accept: GPE to KE to Electrical) [1]

6.
(a) $\text{GPE} = mgh = 200 \times 10 \times 15 = 30,000 \text{ J}$ . [2]
(b) $\text{Power} = \text{Work} / \text{time} = 30,000 / 30 = 1,000 \text{ W}$ (or 1 kW). [2]

7.
(a) $\text{KE} = \frac{1}{2}mv^2 = 0.5 \times 1200 \times (20)^2 = 600 \times 400 = 240,000 \text{ J}$ . [2]
(b) $\text{Work Done} = \text{Force} \times \text{distance}$ .
The work done by brakes equals the loss in KE.
$240,000 = F \times 40$
$F = 240,000 / 40 = 6,000 \text{ N}$ . [2]

8.
(a) $\text{Work} = \text{Force} \times \text{distance} = 50 \times 3 = 150 \text{ J}$ . [1]
(b) $\text{Efficiency} = (150 / 200) \times 100\% = 75\%$ . [2]

9.
(a) $\text{Loss in GPE} = mgh = 0.2 \times 10 \times 0.5 = 1.0 \text{ J}$ . [1]
(b) $\text{Gain in KE} = \text{Loss in GPE}$ (conservation of energy).
$\frac{1}{2}mv^2 = 1.0$
$0.5 \times 0.2 \times v^2 = 1.0$
$0.1 v^2 = 1.0 \rightarrow v^2 = 10 \rightarrow v = \sqrt{10} \approx 3.16 \text{ m/s}$ . [2]

10.
(a) $\text{Work} = mgh = 100 \times 10 \times 10 = 10,000 \text{ J}$ . [1]
(b) $\text{Input Energy} = \text{Power} \times \text{time} = 1000 \times 20 = 20,000 \text{ J}$ .
$\text{Efficiency} = (10,000 / 20,000) \times 100\% = 50\%$ . [2]

11.
(a) $\text{Work} = mgh = 80 \times 10 \times 10 = 8,000 \text{ J}$ . [1]
(b) Work is done against friction (air resistance and friction in bicycle chains/wheels), which dissipates energy as heat and sound. [1]

12. Power is the rate of doing work or the rate of energy transfer. ( $P = E/t$ or $P = W/t$ ). [1]

13.
(a) Gravitational Potential Energy is converted to Kinetic Energy. [1]
(b) $\text{Loss in GPE} = \text{Gain in KE}$
$mgh = \frac{1}{2}mv^2$
$gh = \frac{1}{2}v^2$
$10 \times h = 0.5 \times (25)^2$
$10h = 312.5$
$h = 31.25 \text{ m}$ . [2]

14.
(a) $\text{Time} = 3 \times 60 = 180 \text{ s}$ .
$\text{Energy} = P \times t = 2000 \times 180 = 360,000 \text{ J}$ . [2]
(b) $\text{Wasted} = \text{Total Input} - \text{Useful Output} = 360,000 - 300,000 = 60,000 \text{ J}$ . [1]

15. Some energy is always dissipated/wasted as heat (due to friction) or sound during operation. Therefore, useful output is always less than total input. [1]

16. No, the statement is incorrect.
Power is the rate of doing work. A less powerful machine can do more work if it operates for a significantly longer time. ( $W = P \times t$ ). [2]

17.
(a) $\text{Work} = F \times d = 50 \times 10 = 500 \text{ J}$ . [1]
(b) The work done is converted into internal energy (heat) due to friction, as the kinetic energy of the box remains constant. [1]

18.
(a) Light (Solar) Energy $\rightarrow$ Electrical Energy. [1]
(b) Advantage: Renewable / No pollution / Low operating cost.
Disadvantage: Intermittent (depends on weather/daylight) / High initial cost / Large area required. [2]

19. Some kinetic energy is converted to heat and sound upon impact with the ground and due to air resistance during flight. Thus, the ball has less mechanical energy to convert back to GPE. [1]

20.
$\text{Useful Work Output} = mgh = 500 \times 10 \times 20 = 100,000 \text{ J}$ .
$\text{Total Energy Input} = P \times t = 5000 \text{ W} \times 25 \text{ s} = 125,000 \text{ J}$ .
$\text{Efficiency} = (100,000 / 125,000) \times 100\% = 80\%$ . [3]