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O Level Physics Energy Power Quiz

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Questions

O-Level 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.
Use $g = 10 \text{ m/s}^2$ where necessary.

Section A: Multiple Choice & Short Answer (Questions 1-5)

1. 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

[1]

2. Which of the following statements correctly describes the energy changes when a ball falls freely from a height and hits the ground?
A) Gravitational potential energy $\rightarrow$ Kinetic energy $\rightarrow$ Sound and Heat
B) Kinetic energy $\rightarrow$ Gravitational potential energy $\rightarrow$ Sound
C) Gravitational potential energy $\rightarrow$ Elastic potential energy $\rightarrow$ Kinetic energy
D) Chemical energy $\rightarrow$ Kinetic energy $\rightarrow$ Heat

[1]

3. A 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

[1]

4. State the principle of conservation of energy.

[1]

5. A student pushes a box with a constant force of 50 N along a horizontal floor for a distance of 4 m. Calculate the work done by the student.

Work done = __________________________ J

[1]

Section B: Definitions & Basic Calculations (Questions 6-10)

6. Define power in terms of energy and time.

[1]

7. A car travels at a constant speed on a level road. The engine provides a driving force of 800 N. If the car travels 100 m in 5 seconds, calculate the power developed by the engine.

Power = __________________________ W

[2]

8. Identify the primary energy source for each of the following power stations:
(a) Coal-fired power station: __________________________
(b) Hydroelectric power station: __________________________

[2]

9. A pump lifts water from a reservoir to a tank 10 m above. The pump lifts 50 kg of water every minute. Calculate the weight of 50 kg of water.

Weight = __________________________ N

[1]

10. Using the data from Question 9, calculate the work done in lifting 50 kg of water through 10 m.

Work done = __________________________ J

[2]

Section C: Structured Problems (Questions 11-15)

11. A roller coaster car of mass 600 kg starts from rest at the top of a hill (Point A) which is 30 m above the ground. It travels down to the bottom of the hill (Point B). Assume friction and air resistance are negligible. Calculate the gravitational potential energy of the car at Point A.

Gravitational potential energy = __________________________ J

[2]

12. Referring to the roller coaster in Question 11, state the kinetic energy of the car at Point B and explain your answer.

Kinetic energy = __________________________ J
Explanation: _________________________________________________________________

[2]

13. Calculate the speed of the roller coaster car at Point B.

Speed = __________________________ m/s

[3]

14. An electric lift raises a load of mass 200 kg through a vertical height of 15 m in 20 seconds. Calculate the useful work done in raising the load.

Useful work done = __________________________ J

[2]

15. For the lift in Question 14, the motor has a power input of 2000 W. Calculate the efficiency of the motor.

Efficiency = __________________________ %

[2]

Section D: Data Interpretation & Application (Questions 16-20)

16. The graph below shows the velocity of a cyclist of mass 80 kg (including the bicycle) over a period of 20 seconds on a flat road.

*(Imagine a velocity-time graph:

t=0 to t=5s: Velocity increases uniformly from 0 to 10 m/s.
t=5 to t=15s: Velocity remains constant at 10 m/s.
t=15 to t=20s: Velocity decreases uniformly from 10 to 0 m/s.)*

Calculate the acceleration of the cyclist during the first 5 seconds.

Acceleration = __________________________ m/s²

[2]

17. Calculate the resultant force acting on the cyclist during the first 5 seconds.

Resultant force = __________________________ N

[2]

18. Calculate the kinetic energy of the cyclist at t = 5 s.

Kinetic energy = __________________________ J

[2]

19. During the interval t = 5 s to t = 15 s, the cyclist maintains a constant speed of 10 m/s. The driving force provided by the cyclist is 40 N. Calculate the power developed by the cyclist during this interval.

Power = __________________________ W

[2]

20. A hydroelectric power station uses water falling from a height of 150 m to drive turbines. 1000 kg of water falls through the turbines every second. The generators produce 1.2 MW of electrical power. Calculate the efficiency of the power station.

Efficiency = __________________________ %

[2]

Answers

O-Level Physics Quiz - Energy Power (Answer Key)

1. B
Working:
$GPE = mgh = 500 \times 10 \times 20 = 100,000 \text{ J}$
$Power = \frac{Energy}{time} = \frac{100,000}{10} = 10,000 \text{ W}$

2. A
Reasoning: As the ball falls, GPE converts to KE. Upon impact, KE is converted to sound, heat, and deformation energy.

3. A
Working:
Useful Energy = $80\% \times 500 = 400 \text{ J}$
Wasted Energy = Total Input - Useful Output = $500 - 400 = 100 \text{ J}$

4. Energy cannot be created or destroyed; it can only be transformed from one form to another. (Or: The total energy of an isolated system remains constant.)

5. 200 J
Working:
$Work = Force \times distance = 50 \times 4 = 200 \text{ J}$

6. Power is the rate of doing work or the rate of energy transfer. ( $P = \frac{E}{t}$ or $P = \frac{W}{t}$ )

7. 16,000 W
Working:
$Work = Force \times distance = 800 \times 100 = 80,000 \text{ J}$
$Power = \frac{Work}{time} = \frac{80,000}{5} = 16,000 \text{ W}$
(Alternative: $P = Fv$ , $v = \frac{100}{5} = 20 \text{ m/s}$ , $P = 800 \times 20 = 16,000 \text{ W}$ )

8.
(a) Chemical energy (from coal/fossil fuels)
(b) Gravitational potential energy (of water)

9. 500 N
Working:
$Weight = mg = 50 \times 10 = 500 \text{ N}$

10. 5,000 J
Working:
$Work = Force \times distance = 500 \times 10 = 5,000 \text{ J}$

11. 180,000 J
Working:
$GPE = mgh = 600 \times 10 \times 30 = 180,000 \text{ J}$

12. 180,000 J. By the principle of conservation of energy, assuming no energy losses, all GPE at A is converted to KE at B.

13. 24.5 m/s
Working:
$KE = \frac{1}{2}mv^2$
$180,000 = \frac{1}{2} \times 600 \times v^2$
$180,000 = 300 v^2$
$v^2 = 600$
$v = \sqrt{600} \approx 24.5 \text{ m/s}$

14. 30,000 J
Working:
$Work = mgh = 200 \times 10 \times 15 = 30,000 \text{ J}$

15. 75%
Working:
Useful Power Output = $\frac{Work}{time} = \frac{30,000}{20} = 1,500 \text{ W}$
$Efficiency = \frac{Useful Power Output}{Total Power Input} \times 100\%$
$Efficiency = \frac{1,500}{2,000} \times 100\% = 75\%$

16. 2 m/s²
Working:
$Acceleration = \frac{\Delta v}{\Delta t} = \frac{10 - 0}{5 - 0} = 2 \text{ m/s}^2$

17. 160 N
Working:
$F = ma = 80 \times 2 = 160 \text{ N}$

18. 4,000 J
Working:
$KE = \frac{1}{2}mv^2 = \frac{1}{2} \times 80 \times 10^2 = 40 \times 100 = 4,000 \text{ J}$

19. 400 W
Working:
$P = Fv = 40 \times 10 = 400 \text{ W}$

20. 80%
Working:
Power Input = Energy per second = $mgh/t = 1000 \times 10 \times 150 / 1 = 1,500,000 \text{ J/s} = 1.5 \text{ MW}$
Power Output = 1.2 MW
$Efficiency = \frac{1.2}{1.5} \times 100\% = 80\%$