PRCSS Prelim Ans

2024 4E Physics Prelim Exam Mark Scheme 1 2 3 4 5 6 7 8 9 10 B C B A D C D A A B 11 12 13 14 15 16 17 18 19 20 B D C D B D C A A D 21 22 23 24 25 26 27 28 29 30 A C B C D D A D B B 31 32 33 34 35 36 37 38 39 40 B A C D B C C A C D 1a upward force equals to weight (in magnitude) upward force and weight are opposite in direction / resultant force is zero 1 1 1b F = ma Fup – 250 000(10) = 250 000 (4.0 – 0)/10 Fup – 2 500 000 = 100 000 Fup = 2 600 000 N 1, 1 1 1c Displacement = area under graph = 0.5(15)(4.0) − 0.5(10)(4.0) + 0.5(20)(2.0) = 30 m 1 1 [7] 2a Force per unit area 1 2bi F1/A1 = F2/A2 100/10 = F2/50 F2 = 500 N 1 1 2bii F1d1 = F2d2 100(20) = 500(d2) d2 = 4.0 cm 1 1 2c Pressure will not be transmitted as gas is compressible 1 [6] 3a Metal is a better thermal conductor than glass Energy is transferred out from the boy quicker //reject Energy transferred from metal to surrounding, absorb heat// 1 1 3b Particles at the heated end are vibrating about their fixed positions more vigorously, they collide with neighbouring particles and pass on energy to cause them vibrate about their fixed position also more vigorously. This process continues till the other end. 1 1 3ci 1 3cii Energy transferred to water = energy transferred from ice mc∆θ = mc∆θ + mlf + mc∆θ 150(4.2)(30 – θf) = 50(2.1)(5) + 50(330) + 50(4.2)θf 18900 – 630θf = 525 + 16500 + 210θf 1875 = 840θf 2.2 °C = θf 1,1 1

[8] 4a Disinfection/sterilisation/kill bacteria and viruses/sun-tanning bed/anti- forgery of printed notes 1 4b hinder chemical reaction/ affects cell process/ damage DNA results in cell death, mutations 1 1 4ci 10−8 m 1 4cii v = f λ 300 000 000 = f 10−8 f = 3.0 × 1016 Hz 1 1 [6] 5a Negatively charged 1 5b dirt particles (negatively charged) attract to metal body unlike charges attract (accept like charges repel) (open cover) knock on metal body 1 1 1 [4] 6a //at least 3 field lines with direction shown// 1 6b use a compass 1 6c Iron is magnetic material so the nails get magnetised/ becomes induced magnets Iron nails attracted to the solenoid 1 1 6d No longer attracted to solenoid, (iron) easily demagnetised 1 [5] 7a clockwise 1 7b The current carrying coil experiences forces, in the magnetic field of the magnet / interaction of magnetic field of current-carrying coil and the magnet produces forces on coil forces on each side of the coil are opposite in direction 1 1 7c Soft iron concentrates magnetic field lines Increases the strength of magnetic field 1 1 7d Reverses direction of current in coil every half a revolution 1 [6] 8ai 1 8aii When the magnet (north pole) moves towards the solenoid, the deflection of the galvanometer shows the direction of current in the solenoid Using the right-hand grip rule, the polarity of the solenoid facing the magnet is