VJC 2022 Prelim P3

1 VICTORIA JUNIOR COLLEGE 2022 JC2 PRELIMINARY EXAMINATIONS Higher 2 Name : _________________________________ CT group : ___________ PHYSICS Paper 3 Longer Structured Questions Candidates answer on the Question Paper. No Additional Materials are required. 9749 / 03 0800 – 1000 h 2 Hours READ THESE INSTRUCTIONS FIRST Write your name and CT group at the top of this page. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagrams or graphs. Do not use staples, paper clips, highlighters, 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. 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 1 2 3 4 5 6 Section B 7 8 Total (max. 80) This document consists of 20 printed pages.

2 Data speed of light in free space, c = 3.00 × 108 m s-1 permeability of free space, µo = 4 × 10-7 H m-1 permittivity of free space, o = 8.85 × 10-12 F m-1 (1/(36)) × 10-9 F m-1 elementary charge, e = 1.60 × 10-19 C the Planck constant, h = 6.63 × 10-34 J s unified atomic mass constant, u = 1.66 × 10-27 kg rest mass of electron, me = 9.11 × 10-31 kg rest mass of proton, mp = 1.67 × 10-27 kg molar gas constant, R = 8.31 J mol-1 K-1 the Avogadro constant, NA = 6.02 × 1023 mol-1 the Boltzmann constant, k = 1.38 × 10-23 J K-1 gravitational constant, G = 6.67 × 10-11 N m2 kg-2 acceleration of free fall, g = 9.81 m s-2

3 Formulae uniformly accelerated motion, s = ut + (½) at2 v2 = u2 + 2as work done on/by a gas, W = pV hydrostatic pressure, p = gh gravitational potential, GM r =− temperature /K= /°C+273.15TT pressure of an ideal gas 21 3 Nmpc V=   mean translational kinetic energy of an ideal gas molecule 3 2E kT= displacement of particle in s.h.m., x = xo sin  t velocity of particle in s.h.m., 22 cos () o o v v t xx   = = − electric current I Anvq= resistors in series, R = R1 + R2 + … resistors in parallel, 1/R = 1/R1 + 1/R2+ … electric potential, V = Q/4or alternating current/voltage, x = xo sin  t Magnetic flux density due to a long straight wire d IB   2 0= Magnetic flux density due to a flat circular coil r NIB 2 0= Magnetic flux density due to a long solenoid nIB 0= radioactive decay, x = xoexp(-t) decay constant, 2 1 2ln t=

4 Section A Answer all the questions in the spaces provided. 1. Figure 1.1 below shows a ball of mass 150 g, attached to an elastic cord, being thrown vertically upwards, with a velocity 5.7 m s -1, from the ground. The cord has a spring constant of 45 N m-1. Initially the cord is unstretched but after a while it becomes stretched. The cord obeys Hooke’s law and air resistance is ignored. (a) Given that the maximum height reached by the ball is 1.12 m, calculate the extension of the elastic cord. Explain your working. [3] (b) Hence, determine the length of the unstretched cord. [1] cord is fixed to a point on the ground directly below the body thrown upwards Figure 1.1

5 (c) Sketch, on Figure 1.2, the variation with displacement of the kinetic energy K, gravitational potential energy G and the elastic potential energy E when the mass moves from the ground to maximum height. Label your graphs clearly and indicate on the scale with values from parts (a) and (b). [4] (d) The ball, still attached with the elastic cord, is now being swirled into a vertical circle shown in Figure 1.3. Discuss whether any work is done by the tension, in the cord, acting on the ball. [2] Energy/J displacement/m Figure 1.2 Figure 1.3

6 2. A parallel sound beam is emitted from a source perpendicularly towards a wall 15 cm away. (a) Explain why a stationary wave will be formed between the source and the wall. [2] (b) The source can be considered to be a node. There are only two more nodes between the source and the wall. Draw in the space below a diagram representing the stationary wave. Include the source and the wall in your diagram. [1] (c) The speed of sound is 360 m s-1. Calculate the frequency of the sound. [2] (d) The location of the node nearest (but not at) the source is marked as ‘X’. The source is then replaced with a point source that emits sound uniformly in all directions. (i) When the sound wave travels directly from the point source to location X, it has an amplitude of 3.0 x 10-5 m. Calculate the amplitude of the wave after it has been reflected by the wall and travels back to location X. Assume that no energy is lost when the wave is reflected by the wall. [3]

7 (ii) Calculate the amplitude of the resultant sound wave at location X due to the interference of the wave that comes directly from the point source, and the wave that is reflected by the wall. Explain your reasoning. [2] 3(a) State what is meant by electric field strength. [2] (b) Two point charges A and B are situated a distance 15 cm apart in a vacuum, as illustrated in Fig. 3.1. Fig. 3.1

8 Point P lies on the line joining the charges and is a distance x from charge A. The variation with distance x of the electric field strength E at point P is shown in Fig. 3.2. Fig. 3.2 (i) By reference to the direction of the electric field, state and explain whether the charges A and B have the same, or opposite, signs. [2] (ii) State why, although charge A is a point charge, the electric field strength between x = 3.0 cm and x = 7.0 cm does not obey an inverse-square law. [1]

9 (iii) A proton is at point P where x = 6.0 cm. Use data from Fig. 3.2 to determine the magnitude of the acceleration of the proton. [3] (iv) Use Fig. 3.2 to determine the ratio of the magnitude of charge A to the magnitude of charge B. [3] 4. An electric current consisting of electrons flowing horizontally from left to right through a thin slab of conductor of width 1.5 cm. The slab of conductor is immersed in a uniform magnetic field B of 4.0 mT, which is applied perpendicularly to the slab of conductor, as shown in the diagram below: (a) The speed of the electrons is 0.60 mm s-1. Calculate the magnetic force acting on each electron. [2] - Magnetic field B = 4.0 mT (perpendicular to slab) Electron 1.5 cm

10 (b) Because of the magnetic force, the electrons accumulate on one side of the conductor. Indicate on the diagram above, where the electrons will accumulate. [1] (c) A vertical electric field is created across the slab as a result of the accumulation of electrons. (i) Draw on the diagram above an arrow to represent the electric field. Label it as E. [1] (ii) As more and more electrons accumulate, the electric field gets stronger and stronger. The rate of electron accumulation decreases. Eventually, further electrons do not accumulate anymore, but continue to travel horizontally. 1. Explain why the rate of accumulation of electrons decreases, and why eventually further electrons do not accumulate anymore. [3] 2. Calculate the potential difference across the horizontall sides of the slab of conductor when the accumulation of electrons stops. [3]