2022 RSS Phy Prelims P2 Ans

Riverside Secondary School Prelim Examination 2022 Science for Sec 4E Solutions and Marking Scheme Deduct HALF mark per question or per part of a question for incorrect significant figures given. Deduction is capped at maximum 2 marks per section. Section A ( 50 marks) Qn Answer Marks Remarks 1a  Measure the time taken for 20 complete movements using a stopwatch. Let the time taken be t1.  Repeat the timing of 20 complete movements using the stopwatch. Let the time taken be t2.  Calculate the average time taken, <t>, for 20 complete movements. <t> =  Calculate the average time taken for one complete movement. Average time = [1] [1] [1] Can accept 10 movements 1b the distance moved in the direction of the force along the track [1] 2a 0 to 15 s – curve with increasing gradient to 120 m 15 s to 25 s – straight line from 120 m to 320 m [1] [1]

2b Kinetic energy = = 3.6 x 107 J [1] [1] 2ci Work done is the product of the force and the distance moved in the direction of the force. [1] 2cii Distance = 560 - 320 = 240 m [1] 2ciii Acceleration = = - 0.83 m/s2 Force while train decelerates = 1.8 x 105 x 0.83 = 1.5 x 105 N (2 sf) OR 3.6 x 107 = F x 240 F = .5 x 105 N (2 sf) [1] [1] Accept 1.49 x 105 N (3 sf) 3ai Weight is the force of gravity acting on the object. [1] 3aii Mass = 2.6 x 103 x 0.15 x 2.0 x 10-2 = 7.8 kg Weight = 7.8 x 10 = 78 N [1] [1] 3b Resultant force = (1.3 x 105 – 1.0 x 105) x 0.15 = 4500 N Direction of force is outwards [1] [1] [1] 3c Pressure = 12 x ρ x 10 9.6 x 104 = 12 x ρ x 10 ρ = 800 kg/m3 [1] [1] 4ai Moment = 25 x 0.72 = 18 Nm [1] 4aii Work done = 25 x = 28. 3 J (3 sf) [1] [1]

Or Work done = 25 x = 28. 1 J 4b The moment of force P about hinge is greater than the moment of force F about the same hinge. Since the perpendicular distance of the line of action of P to hinge is greater than F, hence the door rotates. [1] [1] 5a The initial temperature of the oil is higher. The rate of temperature decrease will be higher / the oil loses energy faster when hotter. [1] [1] 5b The attractive forces between molecules draw the molecules closer. Hence, the potential energy of the molecules decreases. The potential energy lost is the thermal energy lost to the freezer. Hence, the temperature of the oil remained constant from t = 3600 s to t = 10 800 s. [1] [1] [1] 5ci Q = mlf = 45 x 10-3 x 5.7 x 104 = 2600 J (2 sf) [1] [1] 5cii Rate = = 0.36 J/s [1] ecf allowed 5d The specific heat capacity of oil in the liquid state is less than oil in solid state. The temperature decreases of oil in liquid state decreases more quickly. Or The rate of decrease of temperature of oil in solid state is slower than that for liquid state because the specific [1] [1]

heat capacity for oil