NYJC 2023 H2 Physics 9749 P1 Answer

NYJC 2023 9749/01/J2Prelim/23 [Turn over NANYANG JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CLASS TUTOR’S NAME CENTRE NUMBER S INDEX NUMBER PHYSICS 9749/01 Paper 1 Multiple Choice 22 September 2023 1 hour Additional Materials: Multiple Choice Answer Sheet READ THESE INSTRUCTIONS FIRST Write in soft pencil. Do not use staples, paper clips, glue or correction fluid. Write your name, class, Centre number and index number in the spaces at the top of this page. There are thirty questions on this paper. Answer all questions. For each question there are four possible answers A, B, C and D. Choose the one you consider correct and record your choice in soft pencil on the separate Answer Sheet. Read the instructions on the Answer Sheet very carefully. Each correct answer will score one mark. A mark will not be deducted for a wrong answer. Any rough working should be done in this booklet. The use of an approved scientific calculator is expected, where appropriate. This document consists of 15 printed pages.

2 NYJC 2023 9749/01/J2Prelim/23 Data speed of light in free space c = 3.00 × 108 m s−1 permeability of free space  = 4 × 10−7 H m−1 permittivity of free space  = 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 K−1 mol−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 Formulae uniformly accelerated motion 21 2s ut at=+ 22 2v u as=+ 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 molecule 3 2E kT= displacement of particle in s.h.m. 0 sinx x t = velocity of particle in s.h.m. 0 cosv v t = 22 0xx=  − electric current =I Anvq resistors in series 12 . . .R R R= + + resistors in parallel 121/ 1/ 1/ . . .R R R= + + electric potential 04 QV r= alternating current/voltage 0 sinx x t = magnetic flux density due to a long straight wire  = 0 2 IB d magnetic flux density due to a flat circular coil = 0 2 NIB r magnetic flux density due to a long solenoid = 0B nI radioactive decay 0 exp( )x x t =− decay constant 1 2 ln2 t =

3 NYJC 2023 9749/01/J2Prelim/23 [Turn over 1 B 6 D 11 B 16 A 21 A 26 D 2 C 7 B 12 A 17 A 22 B 27 C 3 C 8 A 13 D 18 A 23 A 28 D 4 A 9 D 14 A 19 D 24 D 29 A 5 A 10 C 15 D 20 D 25 B 30 A 1 A quantity x is measured many times and the number N of measurements giving a value of x is plotted against x. The true value of the quantity is xo. Which graph best represents precise measurements with poor accuracy? A B C D Ans: B 2 Errors in measurement may be either systematic or random. Which of the following involves random error? A Not allowing for zero error on an analog voltmeter B Not subtracting background count rate when determining the count rate from a radioactive source C Stopping a stopwatch at the end of a race D Using the value of g as 10 N kg-1 when calculating weight from mass Ans: C 3 Two projectiles, X and Y, are launched into the air from the same place on level ground. They reach the same maximum height as shown. Projectile X is launched vertically upwards and projectile Y is launched at an angle to the horizontal. Air resistance is negligible. Which statement is correct? A X and Y are at rest at their maximum heights. B X and Y are launched with the same speed. C X and Y take the same time to return to the ground. D X and Y travel the same distance.

4 NYJC 2023 9749/01/J2Prelim/23 4 A tractor of mass 1000 kg pulls a trailer of mass 1000 kg via a tow -bar. The total resistance to motion has a constant value of 4000 N. One fifth of this resistance acts on the trailer. If the maximum breaking force of the tow-bar is 3000N, what is maximum acceleration of the tractor and trailer? A 2.2 m s-2 B 3.0 m s-2 C 3.8 m s-2 D 7.0 m s-2 Ans: A For the trailer, ΣF = ma Max breaking force – 800 = 1000 a a = (3000 – 800) / 1000 = 2.2 m s-2 5 A cylinder of radius r, made of material A and B, is placed on a rough floor as shown. The portion made of material B has a radius of 0. 45r and a density of ρ that is half that of material A . O is the centre of the cylinder and P is the centre of the portion made of material B. The distance between O and P is 3 r . If the cylinder is entirely made of material A, its weight will be 90 N. A force F is applied horizontally to the top of the cylinder so that O and P are at the same height from the floor as shown. What is the force F required to keep the cylinder in this equilibrium position? A 1.5 N B 2.0 N C 4.5 N D 7.5 N Ans: A If the entire cylinder is A, the system would be in equilibrium without F. With B, and the system requires F to be in equilibrium. Hence, the moment due to F (and the resulting friction) should be equal to that due to the weight of (portion of A that is replaced by B - B). With F in place, translational equilibrium in the horizontal direction requires a friction f equal in magnitude to F but acting in the opposite direction to F. F and f form a couple. Weight of section replaced by (B) = WA - WB = (ρA – ρB )(VB) g = ½ ρA VB g Taking centre of mass of cylinder A as pivot Moment due to the weight of section replaced by B = ½ ρA π(0.45r)2 l g × r/3 = 0.03375r3 π ρA lg Since ρA VA g = ρA π(r)2 l g = 90 N, 0.03375r3 π lg = 3.04 r N Moment due to the couple of F and f = F × 2r Equating the two moments, F = 1.5 N Ans: C X and Y subjected to the same acceleration due to gravity in the vertical direction, so both reach the ground at the same time. Since X and Y reach the same maximum height, they must be launched with the same initial vertical speed (and NOT same speed since Y’s initial vertical speed is usinθ) F r material A material B rough floor O P

5 NYJC 2023 9749/01/J2Prelim/23 [Turn over 6 Two identical uniform rods, each of weight W, are hinged together to form a structure which is resting on a rough floor as shown. If the reaction forces acting on the structure by the floor are R1 and R2, which of the following shows the forces acting on the structure? Ans: D Combine the two W into a single 2 W, situated at the centre of the two W. Then extends the forces for 2W and the two R. There must intersect at one point. This will eliminate option B and C. Option D R1 R2 W W R1 R2 W W R1 R2 W W R1 R2 W W A B C D

6 NYJC 2023 9749/01/J2Prelim/23 To eliminate option A, refer to the FBD of the left rod of A. There must be a force F1 pointing downward and leftward to maintain equilibrium of the left rod. Then, refer to FBD of right rod. There must be a F2 pointing downward and rightward to maintain equilibrium of this rod. But as these two forces are action and reaction pair, they must point in opposite direction, which is not true in the drawing below. Hence option A is not the answer. Option A 7 A student builds a launcher using an elastic cord of negligible mass and natural length of 1.0 m attached to two rigid supports. Assuming that the elastic cord obeys Hooke’s Law with a spri