2023 CGS Phy Prelims P2 Ans

This paper consists of 18 printed pages (including the cover page). CRESCENT GIRLS’ SCHOOL SECONDARY FOUR PRELIMINARY EXAMINATION PHYSICS 6091/02 Paper 2 28 Aug 2023 1 hr 45 min Class: Register No: Name: READ THESE INSTRUCTIONS FIRST Write your name, index number and class in the spaces provided at the top of this page and on all separate answer sheets used. Write in dark blue or black pen. You may use a soft pencil for any diagrams, graphs, tables or rough working. Do not use staples, paper clips, highlighters, glue or correction fluids. Section A (50 marks) Answer all questions. Section B (30 marks) Answer all questions. Question 11 has a choice of parts, answer either one. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Section A /50 Section B /30 TOTAL

2 Crescent 23 6091 S4 SA2 Section A (50 marks) Answer all questions. Write your answers in the spaces provided in the question paper. 1. A vernier calipers is used to measure the diameter of a small cylinder. Fig. 1.1a shows a vernier calipers and Fig. 1.1b shows the main scale and vernier scale of the vernier caliper in detail. The reading for the diameter of the cylinder is 2.15 cm. (a) (i) Describe how Fig. 1.1b shows that the reading is 2.15 cm. [2] • Main scale reading is 2.10 cm. vernier scale reading is 0.05 cm • Add the two values together to obtain 2.15 cm. (ii) State one precaution taken to find an accurate value for the diameter of the cylinder. [1] Check for zero error before using the instrument. Minus the zero error from the observed reading. OR Take a few diameter readings and find the average (b) The length of the cylinder is 0.026 m and its mass is 4.0 g. Calculate the density of the cylinder. Volume = cross sectional area x length = 3.14 x (2.15/2)2 x 2.6 = 9.4345 cm3 Density = mass / volume = 4.0 / 9.4345 = 0.424 g/cm3 density = ……………………… [3] cylinder Fig. 1.1a Fig. 1.1b

3 Crescent 23 6091 S4 SA2 2. A gymnast jumps off from a high bar from A, lands on a trampoline at B and is in contact with the trampoline between B and C. D is the highest position reached by the gymnast as she rises. Fig. 2.1 shows the velocity-time graph for the gymnast. Air resistance is negligible. (a) Table. 2 below is for the direction of motion of the gymnast and the direction of acceleration of the gymnast. Complete Table. 2. [2] direction of motion of gymnast direction of acceleration of gymnast during AB downwards downwards during CD upwards downwards Table. 2 (b) Using the information from Fig. 2.1b, describe the motion of the gymnast between C and D. [1] speed is decreasing at a constant rate/Constant deceleration (c) State how Fig. 2.1 shows that the distance covered between A and B is larger than the distance covered between C and D. [1] The area under the graph between A and B is larger than the area under the graph between C and D. (d) Determine 1 the change in speed of the gymnast between B and C: -4.0 m/s or 4.0 m/s [1] 2 the change in velocity of the gymnast between B and C: 16 m/s or -16 m/s [1]

4 Crescent 23 6091 S4 SA2 3. Fig. 3 shows a section of the roller coaster track in Universal Studios at Sentosa. The total mass of the roller coaster and its passenger is 1000 kg. The speed of the roller coaster at A is 20 m/s. B and C are the bottom and top points of a vertical loop respectively. A is 30 m above B. The roller coaster travels 250 m from A to B and the speed is 22 m/s when it reaches B. (a) State what is meant by the Principle of Conservation of Energy. [1] The Principle of Conservation of energy states that energy cannot be created or destroyed, but can be converted from one form to another. The total energy in an isolated system remains constant. (b) Calculate the kinetic energy of the roller coaster at B. k.e = 𝟏 𝟐 𝒎𝒗𝟐 = 𝟏 𝟐 𝒙 𝟏𝟎𝟎𝟎 𝒙 𝟐𝟐𝟐 = 242 000 J kinetic energy = ……………………… [2] (c) Calculate the work done against friction from A to B. total energy at A = total energy at B + work done against friction GPE at A + ke at A= ke at B + work done against friction (1000 x 10 x 30) + (0.5 x 1000 x 202) = 242 000 + W.D against friction Work done against friction = 258 000 J work done = ……………………. [2] Fig. 3

5 Crescent 23 6091 S4 SA2 4. Fig. 4 shows a ray of light PQRS as it enters and leaves a semi-circular glass block. The speed of light in air is the same as the speed of light in a vacuum, which is 3.0 x 108 m/s. The refractive index of glass is 1.5. (a) Explain why there is no change in the direction of the ray as it enters the block at Q. [1] The angle of incidence is 0⁰, hence angle of refraction is also 0⁰. (b) Calculate the speed of light between Q and R. n = c / v 1.5 = (3 x 108) / v v = 2.0 x 108 m/s speed = …………………………. [2] (c) Another ray passes along TR. On Fig. 4, draw this ray as it leaves the block at R. [1] • Has a smaller r compared to ray RS • Must have arrow (d) A third ray passes along UR and some of the light emerges into the air at R along the surface of the block. (i) On Fig. 4, label the critical angle c. [1] (ii) The block is replaced by another block which has a higher refractive index. State and explain what happens to ray UR at R now. [3] • The new block has a smaller critical angle. • Angle of incidence is now greater than critical angle, and ray is travelling from optically denser to optically less dense medium, • ray UR will now undergo total internal reflection. Fig. 4 (c)

6 Crescent 23 6091 S4 SA2 5. Fig. 5 shows a negatively charged metallic sphere held with an insulated handle. The sphere is brought near an earthed metal plate attached to a galvanometer via a copper wire. (a) On Fig. 5, draw the electric field set up between the sphere and the metal plate. [2] (b) Explain what happens to the charges on the metal plate when the charged sphere is brought near the metal plate. [2] • As like charges repel, • the negative charges of the plate will move away from the charged rod / move to the right and/or flow down the copper wire. (c) Suggest one method to increase the momentary deflection of the galvanometer. [1] Use a sphere with a greater negative charge OR Bring sphere closer to the plate (d) The sphere is now replaced with an identical metal sphere that is positively charged and brought near the metal plate. State any changes to the deflection on the galvanometer. [1] The galvanometer will deflect in the opposite direction/to the right. Fig. 5

7 Crescent 23 6091 S4 SA2 6. Fig. 6 shows a light dependent resistor (LDR) and a battery of e.m.f 6.0 V connected in a circuit. When no light falls on the LDR, its resistance is 3.6 kΩ. In dim light, its resistance is 1.2 kΩ. The maximum resistance of the potential divider, AB, is 600 Ω. The slider X is at the midpoint of AB. (a) State the potential difference across AB. [1] 6.0 V (b) If no light falls on the LDR, calculate (i) the total resistance in the circuit, r