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O Level Combined Science Practice Paper 3

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TuitionGoWhere Practice Paper - Combined Science O-Level (Physical Sciences)

TuitionGoWhere Exam Practice (AI)
Subject: Combined Science (Physics Component)
Level: O-Level
Paper: Practice Paper (Version 3 of 5)
Duration: 1 Hour
Total Marks: 50

Name: ________________________
Class: ________________________
Date: ________________________

Instructions to Candidates

Write your name, class, and date in the spaces above.
Answer all questions.
Write your answers in the spaces provided in this question paper.
The number of marks is given in brackets [ ] at the end of each question or part question.
You may use a calculator.
Take the acceleration of free fall, $g = 10 \text{ m/s}^2$ .

Section A: Structured Questions (30 Marks)

Answer all questions in this section.

1. A student investigates the motion of a trolley down a ramp. Fig. 1.1 shows the setup.

(a) State the difference between speed and velocity.
[2]

(b) The trolley accelerates uniformly from rest. After 4.0 seconds, its velocity is $2.0 \text{ m/s}$ . Calculate the acceleration of the trolley.
[2]

Answer: ________________________ $\text{m/s}^2$

(c) Explain why the trolley does not continue to accelerate indefinitely if the ramp is very long, considering air resistance.
[2]

2. Fig. 2.1 shows a metal block resting on a horizontal table. The weight of the block is $50 \text{ N}$ and the area of contact with the table is $0.02 \text{ m}^2$ .

(a) Calculate the pressure exerted by the block on the table.
[2]

Answer: ________________________ $\text{Pa}$

(b) The block is now placed on a smaller area of contact, $0.01 \text{ m}^2$ . State and explain what happens to the pressure exerted on the table.
[2]

3. A pendulum bob is pulled to one side and released. It swings back and forth.

(a) State the Principle of Conservation of Energy.
[1]

(b) Describe the energy changes that occur as the pendulum bob swings from its highest point to its lowest point.
[2]

(c) In reality, the pendulum eventually stops swinging. Explain where the energy has gone.
[2]

4. Fig. 4.1 shows a ray of light entering a glass block from air. The angle of incidence is $40^\circ$ . The refractive index of the glass is $1.5$ .

(a) Calculate the angle of refraction inside the glass block.
[3]

Answer: ________________________ $^\circ$

(b) State what happens to the speed of light as it enters the glass block from the air.
[1]

5. A girl of weight $450 \text{ N}$ runs up a flight of 20 steps in $10 \text{ s}$ . Each step has a height of $15 \text{ cm}$ .

(a) Calculate the total work done by the girl against gravity.
[3]

Answer: ________________________ $\text{J}$

(b) Calculate the average power developed by the girl.
[2]

Answer: ________________________ $\text{W}$

6. Fig. 6.1 shows a simple circuit containing a battery, a switch, a fixed resistor, and a thermistor.

(a) Define electrical resistance.
[1]

(b) The temperature of the thermistor increases. State and explain the effect on the reading of the ammeter in the circuit.
[3]

7. Sound waves are longitudinal waves.

(a) Describe the motion of air particles when a sound wave passes through them.
[2]

(b) An echo is heard $0.5 \text{ s}$ after a sound is produced. The speed of sound in air is $340 \text{ m/s}$ . Calculate the distance of the reflecting surface from the source.
[3]

Answer: ________________________ $\text{m}$

8. A metal rod is heated at one end.

(a) Explain, in terms of particles and free electrons, how thermal energy is conducted through the metal rod.
[3]

(b) Why is wood a poor conductor of heat compared to metal?
[1]

Section B: Free-Response Questions (20 Marks)

Answer all questions in this section.

9. A car travels along a straight horizontal road. Fig. 9.1 shows the speed-time graph for the car’s motion.

(a) Describe the motion of the car during the first 10 seconds.
[1]

(b) Calculate the acceleration of the car during the first 10 seconds.
[2]

Answer: ________________________ $\text{m/s}^2$

(c) Calculate the total distance travelled by the car in the first 20 seconds.
[3]

Answer: ________________________ $\text{m}$

(d) The mass of the car is $1000 \text{ kg}$ . Calculate the resultant force acting on the car during the first 10 seconds.
[2]

Answer: ________________________ $\text{N}$

10. A student investigates the relationship between the length of a wire and its resistance. The student uses wires of the same material and cross-sectional area but different lengths.

(a) Draw a circuit diagram that the student could use for this investigation. Include a power supply, an ammeter, a voltmeter, and the test wire.
[3]

(b) The student obtains the following results:

Length / m	Resistance / $\Omega$
0.2	1.0
0.4	2.0
0.6	3.0
0.8	4.0

State the relationship between the length of the wire and its resistance.
[1]

(c) Predict the resistance of a wire of length $1.2 \text{ m}$ made from the same material and cross-sectional area.
[1]

Answer: ________________________ $\Omega$

(d) Explain why the wires might become warm during the experiment.
[2]

11. Fig. 11.1 shows a transformer used to step down voltage from $240 \text{ V}$ to $12 \text{ V}$ for a laptop charger. The primary coil has 1000 turns.

(a) Calculate the number of turns on the secondary coil.
[3]

Answer: ________________________ turns

(b) Explain why a transformer does not work with a direct current (d.c.) supply.
[2]

(c) Assuming the transformer is 100% efficient, calculate the current in the primary coil if the current in the secondary coil is $2.0 \text{ A}$ .
[2]

Answer: ________________________ $\text{A}$

Answers

TuitionGoWhere Practice Paper - Combined Science O-Level (Physical Sciences) - Answer Key

Version: 3 of 5
Subject: Combined Science (Physics Component)

Section A: Structured Questions

1. Motion and Forces (a) Speed is a scalar quantity (magnitude only), while velocity is a vector quantity (magnitude and direction). [1] for scalar/vector distinction, [1] for direction mention. (b) $a = \frac{v - u}{t}$ $a = \frac{2.0 - 0}{4.0} = 0.5 \text{ m/s}^2$ [1] for formula/substitution, [1] for answer. (c) As speed increases, air resistance increases. [1] Eventually, air resistance equals the driving force (or component of weight down slope), resulting in zero resultant force and thus zero acceleration (terminal velocity). [1]

2. Pressure (a) $P = \frac{F}{A}$ $P = \frac{50}{0.02} = 2500 \text{ Pa}$ [1] for formula/substitution, [1] for answer. (b) The pressure increases. [1] Because pressure is inversely proportional to area ( $P = F/A$ ); decreasing the area while keeping force constant increases pressure. [1]

3. Energy (a) Energy cannot be created or destroyed, only converted from one form to another. [1] (b) Gravitational potential energy is converted into kinetic energy. [1] (At the lowest point, KE is maximum and GPE is minimum). [1] (c) Energy is lost to the surroundings as thermal energy (heat) and sound due to air resistance and friction at the pivot. [2]

4. Light (a) Using Snell's Law: $n_1 \sin i = n_2 \sin r$ $1.0 \times \sin(40^\circ) = 1.5 \times \sin(r)$ $\sin(r) = \frac{\sin(40^\circ)}{1.5} = \frac{0.6428}{1.5} \approx 0.4285$ $r = \sin^{-1}(0.4285) \approx 25.4^\circ$ [1] for formula, [1] for substitution, [1] for answer ( $25^\circ - 25.4^\circ$ accepted). (b) The speed of light decreases. [1]

5. Work and Power (a) Total height $h = 20 \times 0.15 \text{ m} = 3.0 \text{ m}$ . $\text{Work Done} = \text{Force} \times \text{Distance} = \text{Weight} \times h$ $W = 450 \times 3.0 = 1350 \text{ J}$ [1] for height calc, [1] for formula, [1] for answer. (b) $P = \frac{W}{t} = \frac{1350}{10} = 135 \text{ W}$ [1] for formula, [1] for answer.

6. Electricity (a) Resistance is the ratio of potential difference across a component to the current flowing through it ( $R = V/I$ ). [1] (b) The ammeter reading increases. [1] As temperature increases, the resistance of the thermistor decreases. [1] According to Ohm's Law ( $I = V/R$ ), if resistance decreases and voltage is constant, current increases. [1]

7. Sound (a) Air particles vibrate/oscillate back and forth parallel to the direction of wave propagation. [1] This creates regions of compression and rarefaction. [1] (b) Total distance travelled by sound = $speed \times time = 340 \times 0.5 = 170 \text{ m}$ . Distance to wall = $\frac{170}{2} = 85 \text{ m}$ . [1] for total dist, [1] for dividing by 2, [1] for answer.

8. Thermal Physics (a) Free electrons gain kinetic energy and move rapidly through the metal lattice, colliding with atoms/ions and transferring energy. [1] The atoms/ions also vibrate more vigorously and pass this vibration to neighboring atoms. [1] Metals are good conductors primarily due to the free electrons. [1] (b) Wood does not have free electrons to transfer energy rapidly. [1]

Section B: Free-Response Questions

9. Kinematics and Dynamics (a) The car accelerates uniformly (constant acceleration). [1] (b) $a = \frac{\Delta v}{\Delta t} = \frac{20 - 0}{10} = 2.0 \text{ m/s}^2$ [1] for substitution, [1] for answer. (c) Distance = Area under graph. Area of triangle (0-10s) = $\frac{1}{2} \times 10 \times 20 = 100 \text{ m}$ . Area of rectangle (10-20s) = $10 \times 20 = 200 \text{ m}$ . Total Distance = $100 + 200 = 300 \text{ m}$ . [1] for triangle area, [1] for rectangle area, [1] for sum. (d) $F = ma = 1000 \times 2.0 = 2000 \text{ N}$ [1] for formula/sub, [1] for answer.

10. Resistance Investigation (a) Diagram must include:

Power supply (cell/battery symbol) [1]
Test wire in series with Ammeter [1]
Voltmeter in parallel across the test wire [1]
Switch (optional but good practice) (b) Resistance is directly proportional to length. [1] (c) $6.0 \, \Omega$ . [1] (Since $1.2 \text{ m}$ is double $0.6 \text{ m}$ , R doubles from $3.0$ to $6.0$ ). (d) Electrical energy is converted into thermal energy (heat) due to collisions between moving electrons and the lattice ions of the wire. [2]

11. Transformers (a) $\frac{N_p}{N_s} = \frac{V_p}{V_s}$ $\frac{1000}{N_s} = \frac{240}{12}$ $\frac{1000}{N_s} = 20$ $N_s = \frac{1000}{20} = 50 \text{ turns}$ [1] for formula, [1] for substitution, [1] for answer. (b) Transformers rely on a changing magnetic field to induce a voltage in the secondary coil. [1] Direct current produces a constant magnetic field, so there is no change in magnetic flux linkage, and thus no induced voltage. [1] (c) For 100% efficiency: $P_{in} = P_{out} \Rightarrow V_p I_p = V_s I_s$ $240 \times I_p = 12 \times 2.0$ $240 I_p = 24$ $I_p = \frac{24}{240} = 0.1 \text{ A}$ [1] for formula/equation, [1] for answer.