O-LevelPhysicsForces5054/42 · May/June 2024 · Q314 Marks

A student investigates the balancing of a metre rule which has a load of mass M fixed to it at the 5.0 cm mark. The student: • places a pivot under the 50.0cm mark of the rule • places another load of mass m = 50g on the rule • adjusts the position of the load with mass m = 50g until the rule is as close to balanced as possible as shown in Fig. 3.1. fixed load of mass M bench pivot d 50 cm 0 cm 5 cm 100 cm movable load of mass m metre rule Fig. 3.1 Fig. 3.2 shows the position of the 50g mass when the rule is balanced. metre rule 92 93 96 97 cm view from above 50 g mass Fig. 3.2 (view from above)

(a)(i)Take readings from the rule and use them to determine the position of the centre of the 50 g mass on the rule.[2]
(a)(ii)Calculate the distance d from the centre of the 50g mass to the 50.0cm mark on the rule. Record your answer on the answer line and in Table 3.1 on page 12.[1]
(a)(iii)Calculate the value of 1000/d. Record your answer on the answer line and in Table 3.1 on page 12.[2]
(b)It is difficult to balance the rule exactly. Describe a technique that the student uses to make sure that the value of d is as accurate as possible.[1]
(c)The student repeats the procedure in (a) for values of mass m from 60 g to 100g and records all the readings in Table 3.1. Table 3.1 mass m/g distance d/cm 1000 / 1 50 d cm 60 37.7 26.5 70 32.3 31.0 80 28.2 35.5 90 25.3 39.5 100 22.2 45.0 On the grid provided in Fig. 3.3 on page 13, plot a graph of m on the y-axis against 1000/d on the x-axis. The axes do not need to start from the origin (0, 0). Draw the straight line of best fit.[4]
(d)(i)Calculate the gradient G of your line. Show all working and indicate on the graph the values you use.[2]
(d)(ii)The mass M of the load fixed to the rule can be determined using the equation: M = 22.2 x G Use your value of G from (d)(i) to calculate the mass M of the load fixed to the rule.[1]
(e)Suggest why this method of determining the mass M of the fixed load is unsuitable if a movable load of mass m = 40g is used.[1]

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Mark scheme

Marking points from the official mark scheme (May/June 2024). The mark or mark type is shown in brackets.

[1] 3(a)(i) 93.5 and 95.9 seen;
[1] 3(a)(i) 94.7 (cm);
[1] 3(a)(ii) 44.7;
[1] 3(a)(iii) 22.3714;
[1] 3(a)(iii) value in table given to 3 significant figures ;
[1] 3(b) adjust mass (slowly) until rule tilts one way, adjust again until it (just) tilts the other way ;
[1] 3(c) axes labelled, quantity and unit ;
[1] 3(c) scales linear, not awkward ;
[1] 3(c) points plotted accurately, to the nearest ½ square ;
[1] 3(c) thin best-fit straight line drawn ;
[1] 3(d)(i) values indicated on the graph, ≥ ½ the line used (Δm ≥ 25) ;
[1] 3(d)(i) G = 2.(0) – 2.4 inclusive ;
[1] 3(d)(ii) calculation of M correct from candidate's G;
[1] 3(e) impossible to balance the rule / balance point is beyond the end of the rule ;

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