62_BPGH_2021 4E Prelim PHY P2 ANSWERS

1 Sec 4 Express Physics Prelim Examination 2021 – Marking Scheme Paper 2 Section A (50 marks) Qn Solutions Mark Allocation 1(a) Velocity is a vector quantity and hence it has a magnitude (= 3.0 m/s) and direction (which is due North). A1 1(b) scale : 1cm represent 0.5 m/s magnitude = 2.2 m/s (  0.2cm ) direction = 42 due west from the North ( 2) Alternative method: using cosine rule and sine rule respectively 𝑣 = √22 + 32 − 2(2)(3)𝑐𝑜𝑠45° = 2.1 m/s (sin  / 2.0 = sin(45) / 2.1   = 42  the following will result in loss of marks 1. wrong orientation of the vector diagram 2. labelling length instead of velocity 3. did not indicate angles on vector diagram 4. drew solid lines unnecessarily 5. resultant velocity was not indicated with a double arrow 6. inappropriate scale used, resulting in a small diagram B1 (vector diagram constructed & labelled correctly) A1 A1 2(a)(i) The moment of a force is the product of the force and the perpendicular distance from the pivot to the line of action of the force. B1 Any symbols used must be defined. 2(a)(ii) The filled buckets that cause moments about the axle are: buckets 2, 3 and 4. A1 45 v

2 2(a)(iii) The largest moment is provided by bucket 3 = (weight of water) x (perpendicular distance from the axle to the line of action of the weight) = (40)(10) x (1.6) = 640 Nm M1 A1 3(a) Insert the thermometer into a steam compartment with the bulb of the thermometer above boiling water. The stem of the thermometer with the marked upper fixed point should protrude from the top of the compartment. Use a manometer to check that the pressure inside the compartment is the same as the atmospheric pressure outside. When the level of the mercury in the t hermometer stem remains steady, it indicates the upper fixed point which is the steam point. B2 (deduct 1 mark for any omission of the three important points) 3(b) physical property that changes substance or object involved example volume a liquid resistance electromotive force (spelled out) a metal a thermocouple B1 (any one of the property and the corresponding substance) 3(c) mass of water = m Assumption: Heat lost by water = Heat gain by thermometer and no heat is lost from the water to the surrounding. m x 4.2 x (90-82) = 2.5 x (82-20) m = 4.6 g M1 A1 (a) B2 (correct construction of the 2 incident rays from the line deeper down below the image, incident rays bent towards the normal, arrow actual line on bottom of the floor

3 (Note: Due to refraction, the image line appears shorter than the actual line.) indicated on ray. Deduct 1 mark for any omission or mistake.) 4(b) Since light travels from water to