A-LevelPhysicsForces, density and pressure9702/33 · Oct/Nov 2017 · Q220 Marks

In this experiment, you will investigate the equilibrium of a metre rule supported by springs.

(a)(i)Set up the apparatus as shown in [Fig. 2.1]. Adjust the position of the bosses until the metre rule is parallel to the bench. The loops of string supporting the rule should be vertical and as close to the ends of the rule as possible. The distance between these loops is c.
(a)(ii)Measure and record c. c = cm[1]
(b)Suspend a mass m of 0.100kg from the loop of string as shown in [Fig. 2.2]. The distance between the string loop below boss A and the string loop supporting the mass is x. Move the mass so that x is approximately 80 cm. Adjust the height of boss B until the rule is parallel to the bench as shown in [Fig. 2.2]. The lengths of the coiled sections of the springs are y and z as shown in [Fig. 2.2].
(c)(i)Record m. m = kg
(c)(ii)Measure and record x. x = cm[1]
(c)(iii)Measure and record y. y = cm
(c)(iv)Measure and record z. z = cm[1]
(d)Estimate the percentage uncertainty in your value of z. percentage uncertainty = [1]
(e)(i)Calculate (x - c/2). (x - c/2) = cm[1]
(e)(ii)Calculate (z - y)/m. Give an appropriate unit. (z - y)/m = [1]
(f)Justify the number of significant figures that you have given for your value of (z - y)/m.[1]
(g)(i)Change m to 0.200kg. Adjust the position of the mass and the height of boss B until the value of y is the same as in (c)(iii) and the metre rule is parallel to the bench.
(g)(ii)Repeat (c)(i), (c)(ii), (c)(iv) and (e). m = kg x = cm z = cm (x - c/2) = cm (z - y)/m = [3]
(h)(i)It is suggested that the relationship between x, c, z, y and m is (x - c/2) = k(z - y)/m where k is a constant. Using your data, calculate two values of k. first value of k = second value of k = [1]
(h)(ii)Explain whether your results support the suggested relationship.[1]
(i)(i)Describe four sources of uncertainty or limitations of the procedure for this experiment. 1. 2. 3. 4.[4]
(i)(ii)Describe four improvements that could be made to this experiment. You may suggest the use of other apparatus or different procedures. 1. 2. 3. 4.[4]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2017). The mark or mark type is shown in brackets.

[1] (a)(ii) Value of c in the range 95.0–100.0 cm.
[1] (c)(ii) Value of x in the range 75.0–85.0 cm.
[1] (c)(iv) Value(s) of raw z to the nearest mm.
[1] (d) Percentage uncertainty in z based on absolute uncertainty of 2–5 mm. If repeated readings have been taken, then the uncertainty can be half the range (but not zero) if the working is clearly shown. Correct method of calculation to obtain percentage uncertainty.
[1] (e)(i) Correct calculation of (x – c/2).
[1] (e)(ii) Correct calculation of (z – y) / m and consistent unit e.g. cm kg⁻¹.
[1] (f) Justification for s.f. in (z – y) / m linked to s.f. in z, y and m or (z – y) and m.
[1] (g)(ii) Second value of x.
[1] (g)(ii) Second value of z.
[1] (g)(ii) Quality: second value of z greater than first value of z (provided m in (g) > (c)).
[1] (h)(i) Two values of k calculated correctly.
[1] (h)(ii) Valid comment consistent with calculated values of k, testing against a criterion stated by the candidate.
A (i)(i) Two readings/too few readings/only two readings not enough to draw a (valid) conclusion.
B (i)(i) Difficult to read x/c on rule owing to thickness of string.
C (i)(i) Difficult to measure y/z/spring with reason e.g. parallax, difficult to judge where end of coiled section is/easy to knock/difficult to hold ruler still.
D (i)(i) Difficult to judge/adjust rule to be parallel to bench/horizontal (not 'rule is not parallel to bench').
E (i)(i) Large percentage uncertainty in (z – y).
1 mark for each point up to a maximum of 4.
A (i)(ii) Take more readings (for different added masses) and plot a graph/take more values of k and compare.
B (i)(ii) Use thread/wire/thin(ner) string or any other valid method.
C (i)(ii) Use clamped ruler/use pointer(s) on rule or spring/use (vernier) calipers.
D (i)(ii) Use a (spirit) level/use ruler and set square with detail.
E (i)(ii) Larger difference between masses/larger x value/springs with smaller spring constant.
1 mark for each point up to a maximum of 4.