NJC 2025 H2 Physics Prelim P3SectionA QP

[Turn over NATIONAL JUNIOR COLLEGE SENIOR HIGH 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME SUBJECT CLASS REGISTRATION NUMBER PHYSICS Paper 3 Longer Structured Questions (Section A) Candidate answers on the Question Paper. 9749/03 19 Sep 2025 2 hours No Additional Materials are required. READ THESE INSTRUCTIONS 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, graphs or rough working. 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. 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 / 10 2 / 10 3 / 9 4 / 11 5 / 10 6 / 10 Sub- Total / 60 Section B / 20 Total / 80 H

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4 Answer all the questions in the spaces provided. 1 (a) Define gravitational potential at a point. ……………………………………………………………………………………………………………… …………………………………………………………………………………………………………… [1] (b) The Earth may be considered to be an isolated sphere of radius R with its mass M concentrated at its centre. The variation of gravitational potential φ with distance x from the centre of the Earth is shown in Fig. 1.1. Fig. 1.1 The radius R of the Earth is 6.4 × 106 m. (i) Show that the mass M of the Earth is 6.0 × 1024 kg. [2]

5 [Turn over (ii) A meteorite is at rest at infinity. The meteorite travels from infinity towards the Earth. When the meteorite at a distance 2R above the Earth’s surface, calculate 1. the speed of the meteorite, speed = ………………………… m s−1 [3] 2. the acceleration of the meteorite. acceleration = ………………………… m s−2 [2] (iii) In practice, the Earth is not an isolated sphere because it is orbited by the Moon. Suggest how the speed calculated in (ii)1. will change. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… …………………………………………………………………………………………………… [2] [Total: 10]

6 2 A cylinder that contains a fixed amount of an ideal gas is shown in Fig. 2.1. Fig. 2.1 The cylinder is tightly fitted with a piston, of cross -sectional area A. The piston moves freely in the horizontal direction, trapping the gas within a length x. (a) A gas molecule of mass m travels at a speed of u in the horizontal direction and collides elastically with the piston and the walls of the container. (i) State an expression, in terms of some or all of the symbols defined above, for the magnitude of the change in momentum during each collision. change in momentum = ……………………………… [1] (ii) Hence, show that the average force exerted on the piston by the molecule is 𝑚𝑢2 𝑥 . [1] (b) The gas in the cylinder undergoes a cycle of changes A → B → C → A, as shown in Fig. 2.2. piston of cross-sectional area A cylinder ideal gas x

7 [Turn over Fig. 2.2 (i) Calculate the work done by the gas during the change A → B. work done by the gas = ……………………………… J [2] (ii) Fig. 2.3 is a table of energy changes during one cycle. Complete Fig. 2.3. section of cycle heating supplied to gas / J work done on gas / J increase in internal energy of gas / J A → B B → C −30 C → A zero 3.7 Fig. 4.2 [4] (iii) The net work done by the gas is considered the useful work done of the cycle. The efficiency of this cycle is given by volume V / cm3 pressure p / 105 Pa 20 5 1.0 7.0 A B C

8 𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 = 𝑢𝑠𝑒𝑓𝑢𝑙 𝑤𝑜𝑟𝑘 𝑑𝑜𝑛𝑒 𝑡𝑜𝑡𝑎𝑙 𝑒𝑛𝑒𝑟𝑔𝑦 𝑖𝑛𝑝𝑢𝑡 × 100% Determine the efficiency of the cycle. efficiency = ……………………………… % [2] [Total: 10] 3 (a) State the principle of superposition. ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… …………………………………………………………………………………………………………… [2] (b) Two coherent microwave sources X and Y of frequency 2.5 × 10 10 Hz are a distance of 0.18 m apart in a vacuum, as shown in Fig. 3.1. Fig. 3.1 (not to scale) There is a phase difference of 180° between the waves emitted by the two sources.

9 [Turn over A microwave detector moves along line PQ, which is parallel to the line joining the two sources and 2.3 m away from it. Point O is along line PQ at a position that is equidistant from the two sources. Point A is the first maximum intensity detected when the detector moves from O to A. (i) Show that the wavelength of the microwaves is 0.012 m. [1] (ii) 1. Explain why zero intensity is detected at point O. ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ……………………………………………………………………………………………… [2] 2. Determine the difference in the distances travelled by the microwaves from X to A and from Y to A. difference = ……………………………… m [1] (iii) Use the formula for the double -slit interference of light to calculate the distance between adjacent intensity maxima on line PQ. distance = ……………………………… m [2]

10 (iv) On Fig. 3.1, draw a cross (×) to show the position of a point along line PQ closest to point O where the waves meet with a phase difference of 90°. Label this point B. [1] [Total: 9]