Cambridge A Level Physics 9702 — 2020 Oct/Nov Paper 3 · Variant 1

1 In this experiment, you will investigate the equilibrium of a plastic cup. (a) You have been provided with a cup attached to a string loop. A mass is attached to the cup as shown in Fig. 1.1. string tape cup mass Fig. 1.1 ● Set up the apparatus as shown in Fig. 1.2. stand clamp boss wooden rod set square p bench Fig. 1.2 ● The horizontal distance between the edges of the cup is p, as shown in Fig. 1.2. Measure and record p. p = ......................................................... [1] (b) ● Pour approximately 12 cm3 of water into the measuring cylinder. ● The mass of 1 cm3 of water is 1 g. Determine the mass of water in the measuring cylinder. mass = ........................................................... g ● Gently pour this water from the measuring cylinder into the cup. ● Record the total mass m of water in the cup. m = ............................................................ g ● Measure and record p. p = ............................................................... [1] (c) Using the measuring cylinder, add water to the cup to increase m. Measure and record p. Repeat until you have six sets of values of m and p. Record your results in a table. Include values of m and p in your table. [10] (d) (i) Plot a graph of p on the y-axis against m on the x-axis. [3] (ii) Draw the straight line of best fit. [1] (iii) Determine the gradient and y-intercept of this line. gradient = ............................................................... y-intercept = ............................................................... [2] (e) It is suggested that the quantities p and m are related by the equation p = A m + B where A and B are constants. Using your answers in (d)(iii), determine the values of A and B. Give appropriate units. A = ............................................................... B = ............................................................... [2] [Total: 20] You may not need to use all of the materials provided.

Mark scheme: 1(a) Value(s) of p in the range 9.0–15.0 cm with unit. 1 1(b) Value of m in the range 10.0–14.0 g. 1 1(c) Six sets of readings of m (different values) and p with correct trend and without help from the Supervisor scores 5 marks, five sets scores 4 marks, etc. 5 Range: Δm ⩾ 80 g. 1 Column headings: Each column heading must contain a quantity, a unit and a separating mark where appropriate. The presentation of quantity and unit must conform to accepted scientific convention, e.g. m / g, p / m½. 1 Consistency: All values of p must be given to the nearest mm. 1 Significant figures: All values of m must be given to the same number of significant figures as, or one greater than, the number of s.f. of the m values as recorded in table. 1 Calculation: Values of p are correct. 1 Question Answer Marks 1(d)(i) Axes: Sensible scales must be used, no awkward scales (e.g. 3:10 or fractions). Scales must be chosen so that the plotted points occupy at least half the graph grid in both x and y directions. Scales must be labelled with the quantity that is being plotted. Scale markings should be no more than three large squares apart. 1 Plotting of points: All observations in the table must be plotted on the grid. Diameter of plotted points must be ⩽ half a small square. Points must be plotted to an accuracy of half a small square. 1 Quality: All points in the table must be plotted on the grid. Trend of points must be correct. It must be possible to draw a straight line that is within ±0.1 on the p axis of all plotted points. 1 1(d)(ii) Line of best fit: Judge by balance of all points on the grid about the candidate’s line (at least 5 points). There must be an even distribution of points either side of the line along the full length. Allow one anomalous point only if clearly indicated (i.e. circled or labelled) by the candidate. There must be at least five points left after the anomalous point is disregarded. Lines must not be kinked or thicker than half a small square. 1 Question Answer Marks 1(d)(iii) Gradient: The hypotenuse of the triangle used must be greater than half the length of the drawn line. Method of calculation must be correct, e.g. not Δx / Δy. Gradient sign on answer line matches graph drawn. Both read-offs must be accurate to half a small square in both the x and y directions. 1 y-intercept: Correct read-off from a point on the line substituted correctly into y = mx + c or an equivalent expression. Read-off accurate to half a small square in both x and y directions. or Intercept read directly from the graph, with read-off at x = zero, accurate to half a small square. 1 1(e) Value of A = candidate’s gradient and value of B = candidate’s intercept. The values must not be fractions. 1 Unit for A correct (e.g. cm0.5 g–0.5 or cm½ g–½) and unit for B correct (e.g. cm0.5 or cm½). 1

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2 In this experiment, you will investigate a cardboard shape falling down a wooden board. (a) (i) You have been provided with a wooden board with nails attached. ● Set up the apparatus as shown in Fig. 2.1. label O stand O wooden board boss clamp nails θ bench Fig. 2.1 ● The angle between the wooden board and the bench is θ. Adjust the apparatus until θ is between 80° and 89°. ● Measure and record θ. θ = ....................................................... ° [1] (ii) Calculate sin θ. sin θ = ......................................................... [1] (iii) Justify the number of significant figures that you have given for your value of sin θ. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] (b) (i) ● Firmly press the adhesive putty centrally onto the cardboard shape as shown in Fig. 2.2. cardboard shape adhesive putty Fig. 2.2 ● Flatten the adhesive putty so that it has a thickness of approximately 5 mm. ● Hold the cardboard shape centrally above the wooden board with the adhesive putty touching the board, as shown in Fig. 2.3. O cardboard shape with adhesive putty touching the wooden board Fig. 2.3 ● When the cardboard shape is released, it follows a path between the nails towards the bench. The time between releasing the shape and the shape touching the bench is t. Measure and record t. t = ...................................................... s [2] (ii) Estimate the percentage uncertainty in your value of t. Show your working. percentage uncertainty = ......................................................... [1] (c) Adjust the apparatus and determine the smallest angle at which the shape will still fall to the bottom of the wooden board after release. (i) ● Measure and record θ. θ = ............................................................ ° ● Calculate sin θ. sin θ = ............................................................... [2] (ii) Measure and record t. t = ...................................................... s [2]

Mark scheme: 2(a)(i) Value(s) of raw θ to the nearest degree. 1 2(a)(ii) Correct calculation of sinθ. 1 2(a)(iii) Justification for significant figures in sinθ linked to s.f. in θ. 1 2(b)(i) Value of time t in range 0.5–3.0 s. 1 Evidence of repeat values of t. 1 2(b)(ii) Percentage uncertainty based on an absolute uncertainty in t in range 0.2–0.5 s. If repeat readings have been taken, then the absolute uncertainty can be half the range (but not zero) if the working is clearly shown. Correct method of calculation to obtain percentage uncertainty. 1 2(c)(i) Second value of θ recorded. 1 Second value of θ less than 70.0°. 1 2(c)(ii) Second value of t recorded. 1 Second value of t greater than first value of t. 1 2(d)(i) Two values of k calculated correctly. The final k values must not be fractions. 1 2(d)(ii) Valid comment consistent with the calculated values of k, testing against a criterion stated by the candidate. 1 Question Answer Marks 2(e)(i) A Two readings are not enough to draw a (valid) conclusion (not “not enough for accurate results”, “few readings”). B Difficulty in measuring time t with a reason, e.g. time interval is short/percentage uncertainty is large/difficult to release shape and start stop-watch simultaneously/difficult to judge when to stop timing. C Difficulty linked to the practical set up of the board, e.g. holding with one clamp, board is not square to bench/board is not stable/board tilts to side. D Difficulty linked to release, e.g. force applied varies/starting position may vary/adhesive putty sticks (affects friction). E Difficulty with the angle with reason, e.g. setting or adjusting the angle when changing the clamp/difficult to make fine adjustments to the angle. 1 mark for each point up to a maximum of 4. 4 2(e)(ii) A Take more readings and plot a graph or take more readings and compare k values (not “repeat readings” on its own). B Improved method to measure t, e.g. timer and pressure/contact switch at release point and/or at bottom or video with timer/frame-by-frame. C Improved method to support board, e.g. use more than one clamp/clamp both sides/support with a block. D Improved method of release, e.g. use of a stop/use of a card gate. E Improved method to make fine adjustments to angle, e.g. scissor jack/use of screw thread on a clamp. 1 mark for each point up to a maximum of 4. 4

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