O Level Combined Science Practice Paper 2

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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 2 (Version 2 of 5)
Duration: 1 Hour 15 Minutes
Total Marks: 65
Name: _________________________
Class: _________________________
Date: _________________________

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Instructions to Candidates

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

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Section A: Structured Questions (40 Marks)

Answer all questions in this section.

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

(a) Define acceleration.
[1]
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(b) The trolley starts from rest and reaches a velocity of $4.0 \, \text{m/s}$ in $2.5 \, \text{s}$. Calculate the acceleration of the trolley.
[2]

<br> <br>

Acceleration = _________________________ $\text{m/s}^2$

(c) State one method to reduce friction in this experiment to ensure more accurate results.
[1]
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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 is $0.02 \, \text{m}^2$.

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

<br> <br>

Pressure = _________________________ $\text{Pa}$

(b) The block is now placed on its side, doubling the area of contact. State and explain the effect on the pressure exerted on the table.
[2]
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3. A pendulum bob is pulled to position A and released. It swings through position B (the lowest point) to position C.

(a) State the principle of conservation of energy.
[1]
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(b) Describe the energy changes that occur as the bob moves from position A to position B.
[2]
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(c) At position B, the bob has a kinetic energy of $12 \, \text{J}$ and a mass of $0.5 \, \text{kg}$. Calculate the velocity of the bob at position B.
[3]

<br> <br> <br>

Velocity = _________________________ $\text{m/s}$

4. Fig. 4.1 shows a ray of light traveling from glass into air. The angle of incidence is $30^\circ$ and the angle of refraction is $48^\circ$.

(a) Calculate the refractive index of the glass.
[2]

<br> <br>

Refractive index = _________________________

(b) Explain why the light ray bends away from the normal when entering the air.
[2]
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(c) State the condition required for total internal reflection to occur.
[1]
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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]

<br> <br> <br>

Work done = _________________________ $\text{J}$

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

<br> <br>

Power = _________________________ $\text{W}$

6. Fig. 6.1 shows a simple mercury-in-glass thermometer.

(a) Explain how the thermometer works using the kinetic particle model.
[2]
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(b) State one feature of the thermometer that makes it sensitive to small changes in temperature.
[1]
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7. A metal rod is heated at one end.

(a) Name the primary method of heat transfer through the metal rod.
[1]
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(b) Explain, in terms of particles and electrons, how heat is transferred in metals.
[3]
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8. Fig. 8.1 shows a circuit containing a battery, a switch, a fixed resistor, and a thermistor.

(a) State how the resistance of the thermistor changes as the temperature increases.
[1]
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(b) Explain the effect of increasing temperature on the current in the circuit.
[2]
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9. A student measures the density of an irregular stone.

(a) Describe how the student can determine the volume of the stone using a measuring cylinder and water.
[2]
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(b) The mass of the stone is $50 \, \text{g}$ and its volume is $20 \, \text{cm}^3$. Calculate the density of the stone.
[2]

<br> <br>

Density = _________________________ $\text{g/cm}^3$

10. Fig. 10.1 shows a bar magnet with a plotting compass placed near its North pole.

(a) Draw the direction of the magnetic field line at the position of the compass.
[1]

(b) State two properties of magnetic field lines.
[2]

1. ...........................................................................................................................................
2. ...........................................................................................................................................

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Section B: Free-Response Questions (25 Marks)

Answer all questions in this section.

11. A car travels along a straight road. Fig. 11.1 shows the speed-time graph for the car’s motion.

(a) Describe the motion of the car during the first $10 \, \text{s}$.
[1]
...................................................................................................................................................

(b) Calculate the acceleration of the car between $10 \, \text{s}$ and $20 \, \text{s}$.
[2]

<br> <br>

Acceleration = _________________________ $\text{m/s}^2$

(c) Calculate the total distance traveled by the car in the first $30 \, \text{s}$.
[3]

<br> <br> <br>

Distance = _________________________ $\text{m}$

(d) Explain why the braking distance of a car increases if the road is wet.
[2]
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12. A student investigates the reflection of sound waves. A siren is placed $50 \, \text{m}$ from a large wall.

(a) Explain how an echo is formed.
[2]
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(b) The speed of sound in air is $340 \, \text{m/s}$. Calculate the time taken for the student to hear the echo after the siren sounds.
[3]

<br> <br> <br>

Time = _________________________ $\text{s}$

(c) State one practical application of sound reflection.
[1]
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13. Fig. 13.1 shows a transformer used to step down voltage from $240 \, \text{V}$ to $12 \, \text{V}$. The primary coil has 1000 turns.

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

<br> <br> <br>

Number of turns = _________________________

(b) Explain why a transformer does not work with direct current (d.c.).
[2]
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(c) State one way to increase the efficiency of a transformer.
[1]
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14. A block of ice at $0^\circ\text{C}$ is heated until it becomes water at $0^\circ\text{C}$.

(a) Name the process involved in this change of state.
[1]
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(b) Explain, using the kinetic particle model, what happens to the particles during this process.
[3]
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(c) State why the temperature remains constant during this process despite continuous heating.
[2]
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15. Fig. 15.1 shows a simple electric motor.

(a) State the effect that causes the coil to rotate.
[1]
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(b) Explain the function of the split-ring commutator.
[2]
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(c) State two ways to increase the speed of rotation of the motor.
[2]

1. ...........................................................................................................................................
2. ...........................................................................................................................................

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End of Paper

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

Answer Key & Marking Scheme (Version 2)

Section A: Structured Questions

1. Motion and Acceleration

• (a) Rate of change of velocity. [1]
• (b)
  • Formula: $a = \frac{v - u}{t}$ [1]
  • Substitution: $a = \frac{4.0 - 0}{2.5} = 1.6 \, \text{m/s}^2$ [1]
  • Answer: $1.6 \, \text{m/s}^2$
• (c) Oil the wheels/axle OR use a smoother ramp OR use a trolley with better bearings. [1]

2. Pressure

• (a)
  • Formula: $P = \frac{F}{A}$ [1]
  • Substitution: $P = \frac{50}{0.02} = 2500 \, \text{Pa}$ [1]
  • Answer: $2500 \, \text{Pa}$
• (b)
  • Statement: Pressure decreases. [1]
  • Explanation: Pressure is inversely proportional to area ($P = F/A$). Since force (weight) is constant and area doubles, pressure halves. [1]

3. Energy and Pendulum

• (a) Energy cannot be created or destroyed, only converted from one form to another. [1]
• (b) Gravitational potential energy is converted to kinetic energy. [2] (1 mark for decrease in PE, 1 mark for increase in KE)
• (c)
  • Formula: $KE = \frac{1}{2}mv^2$ [1]
  • Rearrangement: $v = \sqrt{\frac{2 \times KE}{m}}$ [1]
  • Calculation: $v = \sqrt{\frac{2 \times 12}{0.5}} = \sqrt{48} \approx 6.93 \, \text{m/s}$ [1]
  • Answer: $6.93 \, \text{m/s}$ (Accept 6.9)

4. Refraction

• (a)
  • Formula: $n = \frac{\sin i}{\sin r}$ [1]
  • Substitution: $n = \frac{\sin 30^\circ}{\sin 48^\circ} = \frac{0.5}{0.743} \approx 0.67$ Wait, refractive index of glass > 1. The light goes from Glass to Air.
  • Correction: $n_{glass} \sin i = n_{air} \sin r \Rightarrow n_{glass} \sin 30^\circ = 1 \times \sin 48^\circ$.
  • $n_{glass} = \frac{\sin 48^\circ}{\sin 30^\circ} = \frac{0.743}{0.5} = 1.49$ [1]
  • Answer: $1.49$ (Accept 1.5)
• (b) Light travels from a denser medium (glass) to a less dense medium (air), so it speeds up and bends away from the normal. [2]
• (c) Angle of incidence must be greater than the critical angle. [1]

5. Work and Power

• (a)
  • Total height: $h = 20 \times 0.15 \, \text{m} = 3.0 \, \text{m}$ [1]
  • Work done: $W = F \times d = 450 \times 3.0$ [1]
  • Calculation: $1350 \, \text{J}$ [1]
  • Answer: $1350 \, \text{J}$
• (b)
  • Formula: $P = \frac{W}{t}$ [1]
  • Calculation: $P = \frac{1350}{10} = 135 \, \text{W}$ [1]
  • Answer: $135 \, \text{W}$

6. Thermometer

• (a) As temperature increases, mercury particles gain kinetic energy and move/vibrate more vigorously, taking up more space (expansion). [2]
• (b) Thin bore / Thin capillary tube. [1]

7. Heat Conduction

• (a) Conduction. [1]
• (b)
  • Particles at the hot end vibrate faster and collide with neighboring particles, transferring kinetic energy. [1]
  • Metals have free electrons. [1]
  • Free electrons move rapidly through the metal, transferring energy quickly to cooler parts. [1]

8. Thermistor Circuit

• (a) Resistance decreases. [1]
• (b)
  • Total resistance of circuit decreases. [1]
  • Current increases (since $I = V/R$ and V is constant). [1]

9. Density

• (a)
  • Record initial volume of water in cylinder. [1]
  • Submerge stone completely and record new volume. Volume of stone = Final Volume - Initial Volume. [1]
• (b)
  • Formula: $\rho = \frac{m}{V}$ [1]
  • Calculation: $\rho = \frac{50}{20} = 2.5 \, \text{g/cm}^3$ [1]
  • Answer: $2.5 \, \text{g/cm}^3$

10. Magnetism

• (a) Arrow pointing away from the North pole of the magnet (towards the compass South pole if drawn, or generally away from N). [1]
• (b) Any two:
  • They emerge from North and enter South. [1]
  • They never cross. [1]
  • Closer lines indicate stronger field. [1]

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Section B: Free-Response Questions

11. Speed-Time Graph

• (a) Constant acceleration / Uniform acceleration. [1]
• (b)
  • Gradient calculation: $a = \frac{\Delta v}{\Delta t}$ [1]
  • From graph (assumed linear increase from 0 to 10s, then constant? No, Q11b asks for 10-20s. Let's assume graph shows constant speed 10-20s based on typical patterns, or acceleration. Correction based on standard template: If 0-10s is acceleration, 10-20s is often constant speed or deceleration. Let's assume the graph shows velocity constant at $20 \, \text{m/s}$ from 10-20s for this version).
  • Alternative Interpretation for Version 2: Let's assume the graph shows acceleration from 0-10s, then constant velocity 10-20s, then deceleration 20-30s.
  • If constant velocity: Acceleration = $0 \, \text{m/s}^2$. [2]
  • Note to marker: If the graph provided in the actual exam paper shows a slope, calculate gradient. Here, assuming standard "trap" question where students calculate gradient of a flat line.
  • Answer: $0 \, \text{m/s}^2$
• (c) Distance = Area under graph.
  • Area 1 (Triangle 0-10s): $\frac{1}{2} \times 10 \times 20 = 100 \, \text{m}$
  • Area 2 (Rectangle 10-20s): $10 \times 20 = 200 \, \text{m}$
  • Area 3 (Triangle 20-30s, assuming stop): $\frac{1}{2} \times 10 \times 20 = 100 \, \text{m}$
  • Total: $100 + 200 + 100 = 400 \, \text{m}$. [3] (1 mark per correct area segment or final answer)
• (d) Wet road reduces friction between tires and road. [1] This increases braking distance as the decelerating force is smaller. [1]

12. Sound Reflection

• (a) Sound waves travel from source, reflect off the hard surface (wall), and return to the listener. [2]
• (b)
  • Total distance traveled = $2 \times 50 \, \text{m} = 100 \, \text{m}$. [1]
  • Time = $\frac{\text{Distance}}{\text{Speed}}$ [1]
  • $t = \frac{100}{340} \approx 0.294 \, \text{s}$. [1]
  • Answer: $0.29 \, \text{s}$
• (c) Sonar / Echolocation / Ultrasound scanning. [1]

13. Transformer

• (a)
  • Formula: $\frac{N_p}{N_s} = \frac{V_p}{V_s}$ [1]
  • Substitution: $\frac{1000}{N_s} = \frac{240}{12}$ [1]
  • Calculation: $N_s = \frac{1000 \times 12}{240} = 50$ turns. [1]
  • Answer: 50 turns
• (b) Transformers rely on electromagnetic induction. [1] D.C. produces a constant magnetic field, so there is no change in magnetic flux linkage to induce a voltage in the secondary coil. [1]
• (c) Use soft iron core / Use thicker wires (to reduce resistance) / Laminated core. [1]

14. Change of State

• (a) Melting. [1]
• (b)
  • Particles gain energy and vibrate more vigorously. [1]
  • Forces of attraction between particles are weakened/overcome. [1]
  • Particles break free from fixed positions and can slide past each other. [1]
• (c) Heat energy is used to overcome/break the intermolecular forces of attraction, not to increase kinetic energy (temperature). [2]

15. Electric Motor

• (a) Motor effect / Force on a current-carrying conductor in a magnetic field. [1]
• (b) Reverses the direction of current in the coil every half rotation. [1] This ensures the force on the coil acts in the same rotational direction, allowing continuous rotation. [1]
• (c) Any two:
  • Increase current. [1]
  • Use stronger magnet. [1]
  • Increase number of turns on coil. [1]