NJC 2024 H2 Physics Prelim P3 QP

[Turn over NATIONAL JUNIOR COLLEGE SENIOR HIGH 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME SUBJECT CLASS REGISTRATION NUMBER PHYSICS Paper 3 Structured Questions Candidate answers on the Question Paper. 9749/03 13 Sep 2024 2 hours No Additional Materials are required. READ THE INSTRUCTION FIRST Write your subject class, registration number and name 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 a 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 Answers 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. For Examiner’s Use Section A 1 / 9 2 / 7 3 / 10 4 / 13 5 / 8 6 / 6 7 / 7 Section B 8 / 20 9 / 20 H

2 Total (80) This document contains 29 printed pages and 3 blank pages.

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4 Section A Answer all the questions in the spaces provided. 1 (a) Use Newton's laws of motion to explain why a body moving with uniform speed in a circle must experience a force towards the centre of the circle. …………………………………………………………………………………………………………. …………………………………………………………………………………………………………. …………………………………………………………………………………………………………. …………………………………………………………………………………………………………. …………………………………………………………………………………………………………. ……………………………………………………………………………………………………… [3] (b) Fig. 1.1 shows the construction of a simple accelerometer that is used to measure the centripetal acceleration of a car turning into a corner. Fig. 1.1 (not to scale) The two ends A and B of the accelerometer are fixed to the car. A mass M is connected to two identical springs and it moves between A and B with negligible friction. A pointer attached to M indicates the acceleration of the car.

5 [Turn over The car enters the corner at a speed of 25 km h–1. The radius of the path of the car is 7.0 m. (i) Determine the centripetal acceleration of the car. centripetal acceleration = ……………………….…………… m s–2 [2] (ii) The mass M between the springs in the accelerometer is 0.50 kg. A test shows that a force of 1.0 N moves the pointer by 5.0 mm from its equilibrium position. Determine the displacement of the pointer from the equilibrium position when the car is turning into the corner. displacement = ……………………….…………….. mm [2] (iii) End B is nearer to the centre of the bend compared to A. Explain, in terms of forces exerted by the springs, whether the pointer of the accelerometer moves towards end A or B. …………………………………………………………………………………………....….. …………………………………………………………………………………………....….. …………………………………………………………………………………………….….. …………………………………………………………………………………………….. [2] [Total: 9]

6 2 (a) Define gravitational potential at a point. …………………………………………………………………………………………………………. …………………………………………………………………………………………………………. ……………………………………………………………………………………………………… [1] (b) A satellite of mass m is in a circular orbit of radius r1 around the Earth. It is transferred to a new circular orbit of radius r2 as shown in Fig. 2.1 by firing its thrusters. Fig. 2.1 The mass of the Earth is M and the gravitational constant is G. (i) Show that the increase in potential energy EP of the satellite is given by . [1] satellite mass m Earth mass M r1 r2

7 [Turn over (ii) The speed of the satellite at r2 is smaller than at r1. A student claims that by conservation of energy, the decrease in kinetic energy of the satellite is equal to the increase in gravitational potential energy. Explain why the student is not correct. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. …………………………………………………………………………………………….. [2] (c) A rock of mass mr, initially at rest at infinity, falls towards the satellite orbiting at a radius of r2. The gravitational force between the rock and the satellite is negligible. Determine the speed v of the rock as it hits the satellite in terms of G, M, m, mr, r1 and r2. [3] [Total: 7]

8 3 (a) According to the kinetic theory of gases, the average random translational kinetic energy of an ideal gas particle is given by: where k is the Boltzmann constant and T is the thermodynamic temperature of the gas. (i) Using the above expression, show that the root-mean-square speed of the gas particles is given by: where R is the molar gas constant and M is the molar mass. [2] (ii) A sealed canister contains 0.200 mol of oxygen (molar mass = 32 g). An identical canister contains 0.300 mol of nitrogen (molar mass = 28 g) at the same temperature. Assuming ideal gas behaviour, determine the ratio ratio = ………………. [1]

9 [Turn over (b) The root-mean-square speed of particles at the centre of the Sun is 4.85 x 105 m s-1 and the density of the particles in that region is 1.50 x 105 kg m-3. (i) Assuming that the particles behaved like ideal gas, calculate the pressure in that region. pressure = ……………. Pa [2] (ii) The actual pressure at the centre of the Sun is much higher than the value calculated above. This shows that some of the assumptions used in the kinetic theory of gases cannot be applied to the particles in that region of the Sun. State one assumption that is no longer applicable and explain how it leads to the actual pressure being higher than the one calculated above. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………. [2]

10 (c) A fixed mass of ideal gas is made to undergo the processes shown in Fig 3.1 starting from state A. Fig. 3.1 Complete the table below for each of the processes shown in Fig. 3.1. Process w / kJ q / kJ U / kJ A to B 67.2 B to C 0 C to A 31.6 31.6 0 [3] [Total: 10]