2022 VS Phy Prelims P3 Ans

Prelim 2022 P3 Qn Marks 1 (a) MMO Metre rule clamped in stand and aligned vertically with bench using a set- square and Reading taken when mass hanger A is not moving or Repeated readings taken to obtain average height 2 (b) MMO 2.76+2.75+2.82+2.50 4 = 2.71 𝑠 1 (c) MMO MA =60 g 1 (d) PDO 𝑃 = 0.060 ×10 ×1.0 2.71 = 0.221 J/s 1 (e) PDO t1 = 1.40+1.38+1.26+1.42 4 = 1.37 s P1 = 0.070 ×10 ×1.0 1.37 = 0.511 J/s 1 (f) P • the quantities that you should keep constant, ✓ the height h that mass hanger A falls through ✓ mass of mass hanger B ✓ the same type of string across the pulley ✓ the same pulley 1 • a detailed description of how you will perform the experiment, a. Set up the apparatus as shown in Fig. 1.1. b. Adjust the position of the clamp so that the height h = 1.000 m for mass hanger A and mass hanger B is at rest on the floor. c. Carefully place a 10 g slotted mass on mass hanger A and hold this mass hanger in position. d. Release the mass hanger A and start the stop watch. e. Measure and record the mass of mass hanger A, mass hanger B and the average time taken for mass hanger A to fall to the floor in a table. f. Repeat steps (b) to (e) for 5 more sets of readings of average time taken for additional mass added to the mass hanger A. g. Calculate the 1 𝑡2 / s-2 using the values for the average time taken. 1

• a suitable table in which to display your measurements and calculated values (you do not need to enter any data into the table), MA / g MB / g 1/(MA – MB) / g-1 time taken to fall height h t2 / s-2 t1 / s t2 / s t = ( 𝒕𝟏+ 𝒕𝟐) 𝟐 ) / s 1 • a statement of the graph that you would plot to test the relationship, Plot a graph of t2 / s-2 against 1/(MA – MB) / g-1 If the relationship is valid, 1/(MA – MB) will be linearly related to t2 with a positive gradient. 1 • a sketch of the graph that you would obtain if the suggested relationship is correct, 1 • an explanation of how you would obtain a value of the constant k from your graph. Constant k is the gradient of the graph plotted. 1 2 (a) MMO 𝒇 = 𝟏𝟎.𝟎+𝟏𝟎.𝟎 𝟐 f = 10.0 cm 1 t2 / s2 1 (𝑀𝐴− 𝑀𝐵) / g-1

(b) MMO x = 15.0 cm y = 30.0 cm 1 1 (c) MMO 𝑓 = (𝟏𝟓)(𝟑𝟎) 𝟏𝟓+𝟑𝟎 = 10.0 cm (9.0 to 11.0 cm) 1 1 (d) ACE ✓ The lens should be placed upright and parallel to the screen. This can be checked with a set square. ✓ Object must be directed at the centre of the lens ✓ The torchlight (the source), the lens and the screen must lie along a straight line. ✓ Avoid parallax error in reading from ruler scale by looking at right angle to it. 1 (e) ACE The image size becomes smaller and equal to object size, the image distance becomes nearer and equal to object distance. 1 1 3(a) V0 = 1.50 V MMO V0 measured to appropriate no. of d.p. to the nearest 0.05 V with correct units 1 (b) When taking reading from the voltmeter, view the pointer perpendicularly such that it covers its image in the reflecting strip to avoid parallax error. ACE Suggested reason directly addresses precision of apparatus used to record measurement. 1 (d) V = 0.30 V I = 0.03 A MMO V measured to appropriate no. of d.p. to the nearest 0.05 V with correct units I measured to appropriate no. of d.p. to the nearest 0.01 A with correct units 1 1

(e) 𝒙 / cm 𝑽 / V 𝑰 / A 10.0 0.10 0.04 20.0 0.15 0.04 30.0 0.20 0.03 40.0 0.25 0.03 50.0 0.30 0.03 60.0 0.35 0.03 70.0 0.40 0.03 80.0 0.45 0.03 90.0 0.50 0.03 PDO Column headings with quantities 𝑥, 𝑉 and 𝐼 correct units. PDO all values of 𝑥, 𝑉 and 𝐼 recorded to the correct no. of d.p. and s.f. MMO At least 6 sets of data with at least a range of 50.0 cm, and correct trend: as 𝑥 ↑ , 𝑉 ↑ ACE correct measurement of I with correct trend 1 1 1 1

(f) PDO axes labelled with units and correct orientation PDO Suitable scale, not based on 3, 6, 7 etc., with plotted data occupying ≥ half the page PDO all points plotted correctly (points must be ≤ ½ small square from the correct position) PDO best fit line 1 1 1 1

(g) x’ = 65.0 cm ACE Dotted horizontal line drawn from 0.375 V to best fit line, and dotted vertical line drawn from that point to horizontal axis Correct reading of x-coordinate 1 1 (h) 1. R = 2σx’ R = 2 (25.0)(65.0/100) R = 32.5 Ω ACE Correct substitution of x’ from (g), and expressed R in correct no. of s.f. and units. 1 2. There exists experimental errors such as the overheating of wires, kinks and bends in the wire and internal resistance of battery. ACE Suggestion is based on theoretical understanding of the experiment and shows understanding of the limitations in the apparatus used. 1 (i) G = 0.450−0.175 80.0−25.0 = 0.275 55.0 G = 5.00 × 10−3 V/ cm ACE Hypotenuse of gradient triangle larger than half the length of the best fit line Coordinates of gradient triangle shown on graph G computed correctly to the appropriate no. of s.f. 1 1

(j) Motor should be connected in parallel with the resistance wire so that the potential difference across the motor varies by 5.00× 10−3 V /cm along the wire over the range of 0 V, when x = 0 cm, to 0.50 V, when x = 90.0 cm. As 𝑃 = 𝑉2 𝑅 , this varies the power output and thus the speed of the motor. ACE Explanation is clear with reference to results Position of motor correct drawn [do not accept if motor not connected to jockey] 1 1 MMO – 13 PDO – 8 ACE – 13 P – 6 Total: 40 marks