Broadrick Prelim Ans

4E Physics Prelim 2024 Marking Scheme Paper 1 (40 Marks) 1 2 3 4 5 6 7 8 9 10 D D C B B D B C D B 11 12 13 14 15 16 17 18 19 20 D C A B B C A C B A 21 22 23 24 25 26 27 28 29 30 A A B C A B C D A C 31 32 33 34 35 36 37 38 39 40 D C D C B A C B D B Paper 2 Section A (70 Marks) Qn Solution Marks 1 (ai) Scalar quantities have magnitude only while vector quantities have both magnitude and direction. [1] (aii) mass, distance, speed, etc. [1] (b) Vector Diagram Scale clearly indicated Correct parallelogram / tip-to-tail diagram drawn Tension in X = 3.1 N (+/- a range) [1] [1] [1]

2 Qn Solution Marks 2 (a) In the first 2.0 s, the ball has increasing velocity. [1] (b) Terminal velocity = gradient of graph after 2.0 s 50 30 26.7 /3.125 2.375 m s   (+/- a range) [1] [1] (c) Initially the only force acting on the ball is gravitational force pulling it downwards. As the ball falls, gravity accelerates it and its speed increases. As speed increases, air resistance opposing the motion of the ball increases. When the air resistance opposing the motion of the ball is equal to the gravitational force acting on the ball, resultant force is zero. When resultant force is zero, there is no more acceleration and the ball moves at constant speed known as terminal velocity. [1] [1] [1] (d) Graph [1]

3 Qn Solution Marks 3 (a) Taking moments about the pivot, sum of clockwise moments = sum of anticlockwise moments 90 500 30 500 30 16790 F F N      [1] [1] (b) If the radius of wheel Y is increased, the perpendicular distance between the pivot and the force increases. Since Moment = F x d, when the perpendicular distance increases, the force required decreases. [1] [1] (c) 60 100 60 100 10 500100 60 100 10100 1.2500 P t F d d d m             [1] [1] 4 (a) 4 5 4 5 9 4 10 6 10 9 4 10 606 10 A B A B A A F F A A F F N            [1] [1] (b) pressure of air = pressure in liquid column + atm pressure 5 5 5 5 913600(10)( ) 1.0 106 10 9 1.0 106 10 0.368 36.813600(10) B atm B B atm B F gh PA Fgh PA h h m cm                [1] [1] (ci) The difference in mercury level remains unchanged. [1] (cii) The difference in glycerine levels is larger than the difference in mercury levels. [1]

4 Qn Solution Marks 5 (ai) 480 (2 60) 0.025 480 (2 60) 2300000 /0.025 v v v Pt ml l l J kg        [1] [1] (aii) In reality, there is energy transferred to the internal store of the surroundings. Since Latent heat = m x lV, and the mass of water vaporised is less than in an ideal experiment, the latent heat calculated will be larger than the true value. [1] [1] (bi) During boiling, energy is transferred to the substance through work done against the attractive forces between the particles. Only the internal potential energy of the particles is increased. Since the internal kinetic energy of the particles does not increase, the temperature does not change during boiling. [1] [1] (bii)   480 (2 60) 28.5(100 30) (2300000) 480 (2 60) 28.5(100 30) 0.02422300000 v v Pt C ml Pt C ml m m kg                   [1] [1] 6 (a) A transverse wave has a direction of particle vibration that is perpendicular to the direction of wave travel. [1] (b) Amplitude A [1] (ci) 1 1.250.8f Hz  [1] (cii) The closest P and Q can be is ¼ of a wavelength apart. Longest possible wavelength 20 4 80 cm   [1] (ciii) P and Q could be 0.25 wavelengths apart or 1.25 or 2.25 or 3.25 wavelengths apart, thus there are other possible wavelengths. [1]

5 Qn Solution Marks 7 (a) When the angle of incidence in the optically denser medium (water) is 49°, the angle of refraction in the optically less dense medium (air) is 90°. [1] (b) Rays [1] [1] (c) For angles of incidence that are smaller than the critical angle, the light in the water gets refracted at the boundary with air and emerges out of the water in all directions. For angles of incidence that are larger than the critical angle, the light in the water is totally internally reflected and does not emerge out of the water. [1] [1] (d) 8 8 1 sin sin 3.0 10 (sin 49) 2.26 10 / cn v c c v v c c v m s        [1] [1] 8 (a) Since unlike charges attract, the positively charged plaque is attracted to the negatively charged teeth and makes it difficult to remove from the teeth. [1] (bi) The negatively charged head and bristles of the toothbrush repel negative charges on the surfaces of the teeth, causing the electrons to flow through the body and hand. There will be an excess of positive charges on the teeth, causing the teeth to become positively charged. Since like charges repel and the teeth becomes positively charged, the positive charges on the surfaces of the teeth repel the positively charged plaque. Since unlike charges attract, the positive charges on the plaque are also attracted to the negative charges on the head and bristles of the toothbrush. [1] [1] [1]

6 Qn Solution Marks (bii) 3250 10 (5 60) 75 QI t Q C       [1] [1] 9 (a) [1] (bi) 1. Random decay means that no physical or chemical method can cause a radioactive nucleus to emit radiation. 2. Spontaneous decay means that the time between emissions cannot be predicted/ when a radioactive nucleus will emit radiation cannot be predicted. [1] [1] (bii) Nuclide equation [1] [1] (biii) A strontium nucleus has 52 neutrons and 38 protons, while a yttrium nucleus has 51 neutrons and 39 protons. There is a difference of 1 less neutron and 1 more proton, suggesting that the neutron became a proton to maintain the total number of nucleons and an electron to maintain the total relative charge before and after the reaction. [1] [1] (ci) A radioactive source with half-life of millions of years will not decay at a rate that can be measured by the GM counter. [1] (cii) Number of half-lives 87 329  Number of beta-particles emitted 5 3 1.6 10 200002   [1] [1]

7 Qn Solution Marks 10 (a) When the switch is closed, the iron bar is magnetised by the magnetic field in the solenoid and becomes an electromagnet. The iron bar magnetises the paper clips through induced magnetism and hence attracts the iron paper clips. [1] [1] (b) Solenoid [1] (ci) As the current increases, the number of paper clips attracted increases non-proportionately. This shows that the strength of the electromagnet does not increase proportionately with current. [1] [1] (cii) The strength of the magnet increases and then decreases before finally reaching a maximum. OR The strength of the magnet has a maximum / does not increase indefinitely. OR The maximum strength of the electromagnet occurs when the number of clips attracted is 150. [1] (ciii) From the tables, the number of clips attracted for the same magnetisation M is about the same with a difference of one clips or none. Hence M is approximately constant and the data supports the equation. [1] [1] (d) Since steel is a hard magnetic material which is difficult to magnetise, the number of paper clips attracted will be less than in the first experiment. [1] [1]

8 Paper 2 Section B (10 marks) Qn Solution Marks 12 (a) Electrical energy is transmitted at a high voltage so that current bein