SAJC 2022 Prelim P3 QP + Guide

1 SAJC Prelims 2022 9749/03 [Turn Over Class Index Number Name 21S ST. ANDREW’S JUNIOR COLLEGE JC 2 2022 Preliminary Examination _________________________________________________________________________ PHYSICS, Higher 2 9749/03 Paper 3 Longer Structured Questions 15th September 20222 hours Candidates answer on the Question Paper. No Additional Materials are required. _________________________________________________________________________ READ THESE INSTRUCTIONS FIRST Write your name, index number and Civics Group in the spaces at the top of this page. Write in dark blue or black pen on both sides of the paper. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. The use of an approved scientific calculator is expected, where appropriate. Section A Answer all questions. Section B Answer one question only. You are advised to spend one and a half hours on Section A and half an hour on Section B. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 24 printed pages including this page. Data speed of light in free space c = 3.00 x 108 m s-1 For Examiner’s Use Section A 1 / 9 2 / 8 3 / 11 4 / 8 5 / 6 6 / 7 7 / 11 Section B 8 / 20 9 / 20 Total / 80

2 SAJC Prelims 2022 9749/03 [Turn Over permeability of free space o = 4  x 10-7 H m-1 permittivity of free space o = 8.85 x 10-12 F m-1 = (1/(36)) x 10-9 F m-1 elementary charge e = 1.60 x 10-19 C the Planck constant h = 6.63 x 10-34 J s unified atomic mass constant u = 1.66 x 10-27 kg rest mass of electron me = 9.11 x 10-31 kg rest mass of proton mp = 1.67 x 10-27 kg molar gas constant R = 8.31 J K-1 mol-1 the Avogadro constant NA = 6.02 x 1023 mol-1 the Boltzmann constant k = 1.38 x 10-23 J K-1 gravitational constant G = 6.67 x 10-11 N m2 kg-2 acceleration of free fall g = 9.81 m s-2 Formulae uniformly accelerated motion s = u t + ½ a t2 v2 = u2 + 2 a s work done on/by a gas W = p V hydrostatic pressure p =  g h gravitational potential  = r Gm− temperature T / K = T / oC + 273.15 pressure of an ideal gas p = 1 3 Nm V 〈c2〉 mean translational kinetic energy of an ideal gas molecule E = 2 3 kT displacement of particle in s.h.m. x = xo sin  t velocity of particle in s.h.m. v = v0 cos  t v =   22 0 xx − electric current I = Anvq resistors in series R = R1 + R2 + ... resistors in parallel 1 / R = 1 / R1 + 1 / R2 + ... electric potential V = r Q 04 alternating current/voltage x = xo sin  t magnetic flux density due to a long straight wire B = μ0I 2πd magnetic flux density due to a flat circular coil B = μ0NI 2r magnetic flux density due to a long solenoid B = μ0nI radioactive decay x = xo exp (- t) decay constant  = 2/1 2ln t

3 SAJC Prelims 2022 9749/03 [Turn Over Answer all the questions in the space provided. 1 (a) (i) State the principle of moments. ………………………………………………………………………………………… ………………………………………………………………………………………… ……………………………………………………………………………………….[1] (ii) Fig. 1.1 shows an arrangement used to demonstrate the principle of moments. Fig. 1.1 A uniform beam is supported on the edges of two triangular shaped wooden blocks placed on two weighing scales. The weight of the beam is 17.5 N and the distance between the wooden blocks is 800 mm. A metal object of weight 26.5 N is placed 200 mm from one of the blocks. The blocks exert upward forces A and B on the beam. Calculate the force B. B = ………………. N [2] (iii) State the magnitude of the sum of the two forces A and B and explain your answer. .………………………………………………………………………………………… ….……………………………………………………………………………………… ……….……………………………………………………………………………….[2]

4 SAJC Prelims 2022 9749/03 [Turn Over (iv) Describe what happens to the forces A and B as the metal object is gradually moved to the centre of the beam. .………………………………………………………………………………………… .………………………………………………………………………………………… ….……………………………………………………………………………………… ……….……………………………………………………………………………….[2]

5 SAJC Prelims 2022 9749/03 [Turn Over (b) Fig. 1.2 shows a girl supported by two elastic ropes. She is in equilibrium. Her weight is 392 N. Fig. 1.2 Determine the tensions T1 and T2 in the two ropes. tension T1 = ………..… N tension T2 = ………..… N [2]

6 SAJC Prelims 2022 9749/03 [Turn Over 2 (a) One mole of hydrogen at a temperature of 420 K is mixed with one mole of oxygen at 320 K. After a short period of time the mixture is in thermal equilibrium. (i) Explain what is meant by thermal equilibrium. …………………………………………………………………………………[1] (ii) The kinetic theory of gases leads to the derivation of the equation = 2 3 1 cNmpV . Using the formula above and the ideal gas equation, derive an expression for the mean kinetic energy of an ideal gas molecule in terms of the Boltzmann constant, k, and the temperature T. [2] (iii) Hence determine the average kinetic energy of a hydrogen molecule before the two gases are mixed. kinetic energy = …………………………...J [1]

7 SAJC Prelims 2022 9749/03 [Turn Over (b) (i) Two different gases at the same temperature have molecules with different mean square speeds. Explain why this is so. ………………………………………………………………………….……………… …………………………………………………………………….…………………… …………………………….…………………………………….…………………...[2] (ii) Explain why in the earth’s atmosphere, there is hardly any hydrogen, compared to oxygen molecules. ………………………………………………………………………….………………. …………………………………………………………………….……………………. ………………………………………………………………………….……………..... …………………………………………………………………….……………………. …………………………….…………………………………….…………………...[2]

8 SAJC Prelims 2022 9749/03 [Turn Over 3 (a) A mass undergoes simple harmonic motion. For a displacement x that is measured from its equilibrium position, the acceleration a of the mass m is given by the expression a = - 16 m x (i) Explain how the expression leads to the conclusion that the mass is performing simple harmonic motion. .………………………………………………………………………………………… …….…………………………………………………………………………………… .………………………………………………………………………………………… …….…………………………………………………………………………………… ……….……………………………………………………………………………….[3] (ii) Fig. 3.1 shows the variation of the potential energy of the mass with time. Fig. 3.1 Calculate 1. the frequency for the oscillations of the mass, frequency = ........................................ Hz [1] potential energy / mJ time / s 0 2 4 6 8 600

9 SAJC Prelims 2022 9749/03 [Turn Over 2. the mass, mass = ........................................ kg [2] 3. the amplitude of the oscillations. amplitude = ........................................ m [2] 4. Mark a point on Fig. 3.1 between 0 and 4 s and mark it as Z when the mass is exactly mid-way between the equilibrium position and amplitude position. [1] (b) On Fig. 3.2, sketch a labelled graph of the variation of the velocity with time of the mass for 2 periods. Fig. 3.2 [2] velocity / m s-1 time / s 0

10 SAJC Prelims 2022 9749/03 [Turn Over 4 (a) A fire alarm on a wall produces a loud sound during a fire drill in SAJC. The speed and frequency of the sound waves are 330 m s-1 and 5000 Hz resp