EJC 2023 J1 H2 Promo P4 MS

No Marking Instructions Mark 1(a)(i) • Total mass of at least 5 paper clips measured. Average mass of each paper clip to be computed from total mass. 1 Examiner’s Comments Given that 1 paper clip is very light, students should take the measurement of a larger number of paper clips and finding the average. Measuring a larger quantity would reduce the percentage uncertainty of the measured value. • Value of each paper clip < 1.20 g • Value of each paper clip stated to the correct precision and recorded with an appropriate unit. 1 Examiner’s Comments Final value should be given to the same s.f. as the measurement done. 1(a)(ii) • Average of at least 2 readings. • Must be whole number if the average of 2 consecutive numbers given. 1 Examiner’s Comments When asked for any quantity, always repeat the experiment to find average – no difference in this case! 1(b)(i) • Average of at least 2 measurements. • 125° ≤ θ ≤ 155°. • θ recorded to the correct precision (nearest degree) with unit (degree o) 1 Examiner’s Comments Angles must be measured to nearest whole degree! 1(b)(ii) • 2° ≤ ∆θ ≤ 8°. • Correct calculation. • % uncertainty to 2 s.f. • If repeated readings have been taken, then absolute uncertainty can be computed as follows with full working clearly shown: ( )max min 2/θθ θ∆= − . This method is not valid if the computed value ∆θ = 0, or ∆θ ≤ precision of instrument. 1 Examiner’s Comments Common errors: • θθ θ∆= − max min : NOT correct! • ∆θ should be a whole number 1(c)(i) • Value of M calculated correctly with appropriate s.f. (2 or 3) and units. Examiner’s Comments Question well done generally. A common mistake is to omit the unit for mass, g. 1 1(c)(ii) • Clear explanation or working showing how the maximum value of M can be obtained. • V alues of (a)(ii) and (b)(ii) to be explicitly used • Maximum value of M correctly calculated with appropriate s.f. (2 or 3) and units. Examiner’s Comments Question well done generally. Students need to realise that max M requires cos θ to be a minimum. Correspondingly this would require θ to be a maximum. Also, the maximum number of paper clips required found in (a)(ii) should be taken into consideration when finding max M. 1

1(c)(iii) • Average of at least 2 measurements. • Value of θ in (c)(iii) less than the value of θ in (b)(i). • θ is recorded to the correct precision (nearest degree) with unit (degree o) Examiner’s Comments Common errors: • only one reading taken (MUST take repeated reading!), • expressing the angle measured to 0.1 degree (MUST give to whole number!) • omtting the unit for the angle measured (MUST give units!) 1 1(d)(i) • k1 & k2 calculated correctly and given to appropriate s.f. • k1 & k2 given correct units. Examiner’s Comments Common errors: • omitting the unit for k • taking m = 50 g for both θ measured. 1 1 1(d)(ii) • Percentage diffe