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Secondary 1 Science Semestral Assessment 2 (End of Year) Paper 2
Free Sec 1 Science SA2 Paper 2, LongCat Exam version, with questions, answers, and syllabus-aligned practice for Singapore students.
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Answers
Secondary 1 Science – SA2 Practice Paper (Version 2 of 5)
Answer Key and Marking Scheme
Total Marks: 50
Section A: Multiple Choice Questions [10 marks]
1. (d) Speed [1]
- Marking note: Speed = distance ÷ time, making it a derived quantity. Length, time, and mass are base quantities.
2. (b) Reading the scale with the eye directly in line with the marking [1]
- Marking note: Parallax error occurs when the eye is not perpendicular to the scale marking.
3. (d) 60 J [1]
- Working: Work done = Force × Distance = 20 N × 3.0 m = 60 J
4. (b) Chemical energy → Electrical energy → Kinetic energy [1]
- Marking note: The battery stores chemical energy, which is converted to electrical energy, which then drives the motor to produce kinetic energy.
5. (b) virtual, upright, and 15 cm behind the mirror [1]
- Marking note: A plane mirror always produces a virtual, upright image at the same distance behind the mirror as the object is in front.
6. (a) 16.7 m/s [1]
- Working: Average speed = 120 km ÷ 2 h = 60 km/h = 60 × (1000/3600) = 16.7 m/s (to 3 s.f.)
7. (b) only within the elastic limit of the spring [1]
- Marking note: Hooke's law states that extension is proportional to force only within the elastic limit.
8. (b) Particles are closely packed in a fixed arrangement and vibrate about fixed positions. [1]
9. (b) conduction [1]
- Marking note: Conduction is the transfer of thermal energy through a material without the bulk movement of the material itself.
10. (b) The angle between the incident ray and the normal [1]
- Marking note: The angle of incidence is always measured from the normal, not from the surface.
Section B: Structured Questions [25 marks]
11.
(a) Resultant force = 45 N − 15 N = 30 N in the direction of motion [2]
- Marking: 1 mark for correct subtraction, 1 mark for correct answer with direction or correct magnitude.
- Common mistake: Students may add the forces instead of subtracting.
(b) Work done = Force × Distance = 45 N × 4.0 m = 180 J [2]
- Marking: 1 mark for correct formula/substitution, 1 mark for correct answer.
- Note: Use the pushing force (45 N), not the resultant force.
(c) Kinetic energy (or kinetic energy and thermal energy due to friction) [1]
- Marking note: Accept "kinetic energy" or "kinetic energy and thermal energy." The work done by the resultant force increases the kinetic energy of the trolley.
12.
(a) The cyclist accelerates (or speeds up) uniformly from rest to 6 m/s. [1]
(b) Acceleration = (v − u) ÷ t = (6 − 0) ÷ 4 = 1.5 m/s² [2]
- Marking: 1 mark for correct substitution, 1 mark for correct answer with unit.
(c) Total distance = area under the speed-time graph [1]
- Area = area of triangle (0–4 s) + area of rectangle (4–8 s) + area of triangle (8–10 s)
- = (½ × 4 × 6) + (4 × 6) + (½ × 2 × 6)
- = 12 + 24 + 6
- = 42 m [2]
- Marking: 1 mark for correct method (area under graph), 1 mark for correct final answer.
13.
(a) The speed of light decreases (or slows down). [1]
(b) Diagram should show: [3]
- A normal (dashed line perpendicular to the surface) at the point of incidence
- Incident ray in air at 40° to the normal
- Refracted ray in glass bending towards the normal (angle of refraction < 40°)
- Light ray emerging from the opposite face, bending away from the normal, parallel to the incident ray
- Marking: 1 mark for normal, 1 mark for correct bending at both surfaces, 1 mark for correct labelling.
(c) Light travels slower in glass than in air. [1] When light enters a denser medium (glass), it slows down and bends towards the normal. [1]
- Marking: 1 mark for stating speed decreases, 1 mark for linking this to bending towards the normal.
14.
(a) Work done = 0 J [1]
- Explanation: The force applied by the student is vertical (upwards, to support the bag), but the displacement is horizontal. Since the force and displacement are perpendicular, no work is done by the student in the direction of displacement. [1]
- Common mistake: Students may calculate 50 N × 10 m = 500 J without considering the direction of force.
(b) Work done = Force × Distance = 50 N × 1.5 m = 75 J [2]
- Marking: 1 mark for correct substitution, 1 mark for correct answer.
(c) Gravitational potential energy [1]
15.
(a) Points A and B [1]
- Explanation: At the highest points (A and B), the bob is at its maximum height, so it has maximum gravitational potential energy. The bob momentarily stops at these points. [1]
(b) The lowest point (bottom of the swing) [1]
- Explanation: At the lowest point, the bob is moving at its fastest speed, so it has maximum kinetic energy. All the gravitational potential energy has been converted to kinetic energy. [1]
(c) The principle of conservation of energy (or law of conservation of energy) [1]
- Marking note: Energy is converted between gravitational potential energy and kinetic energy, but the total energy remains constant (in the absence of air resistance).
Section C: Data-Based and Application Questions [15 marks]
16.
(a) Extension = Length − Original length = 16.0 − 10.0 = 6.0 cm [1]
(b) Graph: [3]
- Marking: 1 mark for correct scale and labelled axes (Extension/cm on y-axis, Mass/g on x-axis), 1 mark for correct plotting of points, 1 mark for best-fit straight line through the first 5–6 points.
- Note: The graph should be a straight line up to 500 g, then curve or deviate at 600 g.
(c) From the graph, extension of 7.0 cm corresponds to a mass of approximately 350 g (accept 340–360 g). [1]
(d) The spring no longer obeys Hooke's law beyond 500 g. [1]
- Explanation: Up to 500 g, the extension increases uniformly (by 2.0 cm for each 100 g added). At 600 g, the extension is 13.0 cm (from 10.0 to 23.0 cm), which is 3.0 cm more than the previous increment of 2.0 cm. This non-uniform increase indicates the elastic limit has been exceeded. [1]
17.
(a) Minimum work = Force × Vertical height = 600 N × 2.0 m = 1200 J [2]
- Marking: 1 mark for correct substitution, 1 mark for correct answer.
(b) The ramp reduces the force needed (a smaller force is required to push the crate up the ramp than to lift it vertically). [1]
(c) Friction between the crate and the ramp (or energy is lost as thermal energy due to friction). [1]
18.
(a) The wax blobs on the copper rod will melt and fall off first (or more quickly) than those on the iron rod. [1] The wax closest to the heated end melts first, followed by those further along the copper rod. [1]
(b) Copper is a better conductor of heat than iron. [1] In conduction, thermal energy is transferred through the vibration and collision of particles. Copper transfers thermal energy more efficiently, so heat travels along the copper rod faster, melting the wax blobs sooner. [1]
(c) Any one of: length of the rod, diameter/thickness of the rod, initial temperature, amount of wax on each blob, or heat source temperature. [1]
- Marking note: Accept any one valid controlled variable.
19.
(a) Acceleration = gradient of the speed-time graph (0–4 s) = (8 − 0) ÷ (4 − 0) = 2.0 m/s² [2]
- Marking: 1 mark for correct substitution, 1 mark for correct answer with unit.
(b) Total distance = area under the graph [1]
- Area = triangle (0–4 s) + rectangle (4–12 s) + triangle (12–16 s)
- = (½ × 4 × 8) + (8 × 8) + (½ × 4 × 8)
- = 16 + 64 + 16
- = 96 m [2]
- Marking: 1 mark for correct method, 1 mark for correct final answer.
(c) The toy car is decelerating (or slowing down) uniformly from 8 m/s to rest. [1]
20.
(a) Gravitational potential energy = mgh = 0.10 × 10 × 2.0 = 2.0 J [2]
- Marking: 1 mark for correct substitution, 1 mark for correct answer with unit.
(b) Some of the kinetic energy (or mechanical energy) is converted to thermal energy and sound energy when the ball hits the ground. [1] Because some energy is lost to the surroundings, the ball has less kinetic energy after the bounce and therefore cannot reach the original height. [1]
- Marking note: Accept any valid form of energy loss (thermal, sound, deformation energy).
(c) Energy cannot be created or destroyed; it can only be converted from one form to another. [1]
- Marking note: Accept equivalent wording such as "The total energy in a closed system remains constant."
End of Answer Key