Secondary 2 Science Semestral Assessment 2 (End of Year) Paper 5

SA2 Practice Paper — Science Secondary 2 (Version 5)

Answer Key & Marking Scheme

Section A — Multiple Choice (10 marks)

Section A Total: 10 marks

Section B — Structured Response (25 marks)

11.

(a) [1] The height / angle of the ramp (or the slope of the ramp).
Marking note: Accept any reasonable independent variable relevant to the experiment. Do NOT accept "speed" or "time" as the independent variable.

(b) [1] Any one controlled variable, e.g., the same trolley used / the same starting point / the same surface of the ramp.
Marking note: Must be a variable that could affect the outcome and is deliberately kept constant.

(c) [1] The trolley is accelerating / speeding up. The increasing dot spacing indicates that the trolley covers a greater distance in each successive time interval.
Marking note: Award the mark for stating acceleration with a valid reason linked to increasing spacing.

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12.

(a) [2] The reflected ray must be drawn on the opposite side of the normal, with angle of reflection = angle of incidence. Both angles must be clearly labelled.
Marking: 1 mark for correct reflected ray direction; 1 mark for correctly labelling both angles.

(b) [2] The angle of incidence is equal to the angle of reflection. AND The incident ray, the reflected ray, and the normal all lie in the same plane.
Marking: 1 mark for each correct statement. Accept equivalent wording.

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13.

(a) [2]
Working:
Q = mcΔT
Q = 0.5 × 460 × (85 − 25)
Q = 0.5 × 460 × 60
Q = 13,800 J (or 13.8 kJ)

Marking: 1 mark for correct substitution; 1 mark for correct final answer with unit.

(b) [1] Assumption: No thermal energy is lost to the surroundings / all the energy supplied goes into heating the metal block.
Marking note: Accept any reasonable assumption, e.g., "specific heat capacity is constant over the temperature range."

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14.

(a) [2]
Working:
Energy = Power × Time
E = 75 W × 8 h = 600 Wh = 0.60 kWh

Marking: 1 mark for correct substitution; 1 mark for correct answer in kWh.

(b) [3]
Working:

• Kettle: E = 2000 W × 0.5 h = 1000 Wh = 1.00 kWh
• Fan: E = 0.60 kWh (from part a)
• Lamp: E = 15 W × 6 h = 90 Wh = 0.09 kWh

Total energy = 1.00 + 0.60 + 0.09 = 1.69 kWh

Total cost = 1.69 × $0.25 = **$0.4225 ≈ $0.42**

Marking: 1 mark for calculating energy of kettle; 1 mark for calculating energy of lamp; 1 mark for correct total cost. Accept $0.42 or$0.423.

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15.

(a) [3]
Step 1: Use a magnet to attract and remove the iron filings from the mixture. (Technique: magnetic separation)
Step 2: Add water to the remaining mixture of sand and salt and stir to dissolve the salt. (Technique: dissolution)
Step 3: Filter the mixture. The sand remains on the filter paper as the residue, and the salt solution passes through as the filtrate. (Technique: filtration)
Step 4: Heat the salt solution (filtrate) to evaporate the water, leaving behind solid salt. (Technique: evaporation)

Marking: 1 mark for using a magnet to remove iron filings; 1 mark for dissolving salt in water and filtering to separate sand; 1 mark for evaporating the filtrate to obtain salt. Steps must be in a logical order.

(b) [1] Filtration is used because sand is insoluble in water and remains as a solid, while the salt solution passes through the filter paper. It separates an insoluble solid (sand) from a liquid (salt solution).
Marking note: Award the mark for stating that sand is insoluble and is separated from the liquid by the filter paper.*

[4]

16.

(a) [1]
R_total = R₁ + R₂ = 4 + 6 = 10 Ω

(b) [2]
Working:
V = IR
V = 0.5 × 10 = 5.0 V

Marking: 1 mark for using V = IR; 1 mark for correct answer with unit.

(c) [2]
Working:
P = I²R
P = (0.5)² × 6 = 0.25 × 6 = 1.5 W

Marking: 1 mark for correct formula/substitution; 1 mark for correct answer with unit.

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17.

(a) [2] The bob has maximum kinetic energy at Point B (the lowest point). This is because at Point B, the bob is at its lowest height, so gravitational potential energy is at its minimum. By conservation of energy, the kinetic energy is at its maximum, and the bob is moving fastest.
Marking: 1 mark for identifying Point B; 1 mark for explaining using energy conversion (GPE → KE).

(b) [1] The principle of conservation of energy — total mechanical energy (KE + GPE) remains constant, so the bob returns to the same height.
Marking note: Accept "conservation of energy" or "conservation of mechanical energy."

[3]

18.

(a) [1] The food colouring spreads faster in the hot water.

(b) [2] In hot water, the water particles have more kinetic energy and move faster. This causes the food colouring particles to diffuse (spread out) more quickly as they are carried along by the faster-moving water particles. The rate of diffusion is higher at higher temperatures.
Marking: 1 mark for stating that particles have more kinetic energy / move faster at higher temperature; 1 mark for linking this to faster diffusion/spreading.

[3]

Section C — Data-Based & Extended Response (15 marks)

19.

(a) [2] The cyclist is accelerating during the interval 0 to 4 seconds. The speed increases from 0 to 6.0 m/s during this time, which means the velocity is changing — the cyclist is accelerating.
Marking: 1 mark for identifying the correct interval (0–4 s); 1 mark for explaining that speed is increasing.

(b) [3]
Working: The total distance is the area under the speed-time graph. The graph can be divided into sections:

• 0–2 s: Triangle = ½ × 2 × 3.0 = 3.0 m
• 2–4 s: Trapezium = ½ × (3.0 + 6.0) × 2 = 9.0 m
• 4–6 s: Rectangle = 6.0 × 2 = 12.0 m
• 6–8 s: Rectangle = 6.0 × 2 = 12.0 m
• 8–10 s: Trapezium = ½ × (6.0 + 4.0) × 2 = 10.0 m
• 10–12 s: Trapezium = ½ × (4.0 + 2.0) × 2 = 6.0 m
• 12–14 s: Triangle = ½ × 2 × 2.0 = 2.0 m

Total distance = 3.0 + 9.0 + 12.0 + 12.0 + 10.0 + 6.0 + 2.0 = 54.0 m

Marking: 1 mark for correct method (area under graph); 1 mark for correct calculation of at least 4 sections; 1 mark for correct total. Accept 53–55 m if rounding differences occur.

(c) [2]
Working:
KE = ½mv²
KE = ½ × 70 × (6.0)²
KE = ½ × 70 × 36
KE = 1,260 J

Marking: 1 mark for correct substitution; 1 mark for correct answer with unit.

(d) [2] The kinetic energy of the cyclist has been converted to thermal energy (heat) in the brakes and between the tyres and the road due to friction. The total energy is conserved — it is not lost but converted to other forms.
Marking: 1 mark for stating KE is converted to thermal energy / heat; 1 mark for mentioning friction or conservation of energy.

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20.

(a) [2] As the angle of the ramp increases, the force needed to pull the block up also increases. The relationship is directly proportional / positive correlation — the greater the angle, the greater the force required.
Marking: 1 mark for stating that force increases with angle; 1 mark for describing the relationship (directly proportional / positive correlation).

(b) [2] The force needed at 60° would be greater than 14.5 N (accept any reasonable value, e.g., 16–18 N). This is because as the angle increases, a larger component of the block's weight acts along the ramp, requiring a greater pulling force to overcome it.
Marking: 1 mark for predicting a value greater than 14.5 N; 1 mark for explaining that the component of weight along the ramp increases with angle.

(c) [2] Limitation: It is difficult to pull the block at a perfectly constant speed, which introduces error in the force readings.
Improvement: Use a motorised pulley system to pull the block at a constant speed, or take multiple readings and calculate the average force.
Marking: 1 mark for a valid limitation; 1 mark for a relevant improvement.

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END OF ANSWER KEY

Paper Total: 50 marks