A-LevelPhysicsPhysical quantities and units9702/33 · Feb/Mar 2017 · Q220 Marks

In this experiment, you will investigate the friction between string and a plastic pipe.

(a)(i)Select the pipe with the larger diameter.
(a)(ii)The outside diameter of the pipe is D, as shown in Fig. 2.1. Take measurements to find D. Record D. D = cm [2][2]
(b)(i)Write down the mass m of the newton-meter as written on the card. m = kg
(b)(ii)Calculate the weight W of the newton-meter using the expression W = mg where g = 9.81 Nkg⁻¹. W = N [1][1]
(b)(iii)Justify the number of significant figures you have given for your value of W. [1][1]
(c)(i)Use the stand, boss and clamp to hold the pipe securely parallel to the bench. Adjust the height of the boss until the pipe is approximately 50cm above the bench. Assemble the rest of the apparatus as shown in Fig. 2.2, with the string passing over the pipe.
(c)(ii)Slowly pull down the hook of the newton-meter so that the mass is lifted off the bench and continues to rise.
(c)(iii)As the mass is rising steadily, record the reading F from the newton-meter. F = N [2][2]
(d)Estimate the percentage uncertainty in your value of F. percentage uncertainty = [1][1]
(e)Repeat (a)(ii) and (c) using the smaller diameter plastic pipe. D = cm F = N [3][3]
(f)(i)It is suggested that the relationship between F, W and D is (F + W)² = k √D where k is a constant. Using your data, calculate two values of k. first value of k = second value of k = [1][1]
(f)(ii)Explain whether your results in (f)(i) support the suggested relationship. [1][1]
(g)(i)Describe four sources of uncertainty or limitations of the procedure for this experiment. 1. 2. 3. 4. [4][4]
(g)(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][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 (Feb/Mar 2017). The mark or mark type is shown in brackets.

[1] All raw values of D to nearest 0.1 cm.
[1] Evidence of repeat readings.
[1] Correct calculation of W.
[1] Justification for s.f. in W linked to s.f. in m and g.
[1] Raw values of F to nearest 0.1 N.
[1] Evidence of repeat readings of F.
[1] Absolute uncertainty in F of 0.2 to 0.5N and correct method of calculation to obtain percentage uncertainty. If repeated readings have been taken, then the absolute uncertainty can be half the range (but not zero if values are equal).
[1] D for second pipe.
[1] F for second pipe.
[1] Quality: Both F > 3 N and < 10 N.
[1] Two values of k calculated correctly.
[1] Sensible comment relating to the calculated values of k, testing against a criterion specified by the candidate.
[4] α Two readings are not enough to draw a valid conclusion. ∞ Difficult to measure diameter with reason, e.g. diameter varies/e.g. ends not square. ∞ Large uncertainty in D. ∞ Difficult to pull hook down steadily. ∞ Difficult to estimate average force during movement/F changes during movement. ∞ Newton-meter collides with mass/observation time too short. ∞ String slides off pipe/slides down pipe. 1 mark for each point up to a maximum of 4.
[4] α Take more readings and plot a graph/calculate more k values and compare. ∞ Use (vernier) calliper/measure between two blocks/use micrometer. ∞ Improved pulling method to give constant speed, e.g. use a motor/e.g. use a known weight. ∞ Record images (or video) of the reading (or measurement) and play back. ∞ Use longer string with taller stand. ∞ Use two stands/support pipe on rod/use spirit level to ensure pipe is horizontal/use groove around pipe (to guide string). 1 mark for each point up to a maximum of 4.