A-LevelPhysicsForces, density and pressure9702/33 · May/June 2020 · Q120 Marks
In this experiment, you will investigate the equilibrium of a metre rule. (a) You have been provided with a metre rule with a string attached to it. • Set up the apparatus as shown in Fig. 1.1. [Figure 1.1] • Add masses to the mass hanger so that mass m is 80 g. • Adjust the pivot so that it is 5mm from end B of the rule. The distance between the string at end A and the pivot is L. • Measure and record L. L = • Adjust the string loop supporting the 100g mass so that it is approximately 60cm from end A. • Hold the rule at end A so that the rule is approximately horizontal. • Adjust the position of the string loop to find the position where end A is just about to move upwards when the rule is released. The distance between the string at end A and the string loop is y₁ as shown in Fig. 1.2. [Figure 1.2] • Measure and record y₁. y₁ = • Adjust the position of the string loop to find the position where end A is just about to move downwards when the rule is released. The distance between the string at end A and the string loop is y2. • Measure and record y2. y₂ = • Calculate y where y = (y₁ + y₂) / 2 y =
- (a)You have been provided with a metre rule with a string attached to it. • Set up the apparatus as shown in Fig. 1.1. [Figure 1.1] • Add masses to the mass hanger so that mass m is 80 g. • Adjust the pivot so that it is 5mm from end B of the rule. The distance between the string at end A and the pivot is L. • Measure and record L. L = • Adjust the string loop supporting the 100g mass so that it is approximately 60cm from end A. • Hold the rule at end A so that the rule is approximately horizontal. • Adjust the position of the string loop to find the position where end A is just about to move upwards when the rule is released. The distance between the string at end A and the string loop is y₁ as shown in Fig. 1.2. [Figure 1.2] • Measure and record y₁. y₁ = • Adjust the position of the string loop to find the position where end A is just about to move downwards when the rule is released. The distance between the string at end A and the string loop is y2. • Measure and record y2. y₂ = • Calculate y where y = (y₁ + y₂) / 2 y =[3]
- (b)Increase m. Measure the new values of y₁ and Y2. Repeat until you have five sets of values of m, y₁ and Y2. Record your results in a table. Include values of y in your table.[8]
- (c)(i)Plot a graph of y on the y-axis against m on the x-axis.[3]
- (c)(ii)Draw the straight line of best fit.[1]
- (c)(iii)Determine the gradient and y-intercept of this line. gradient = y-intercept =[2]
- (d)It is suggested that the quantities y and m are related by the equation y = Am + B where A and B are constants. Using your answers in (c)(iii), determine the values of A and B. Give appropriate units. A = B =[2]
- (e)Theory suggests that B = L - (RA)/2 where R is the mass of the metre rule. Determine a value for R. Give your answer to three significant figures. R =[1]
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 (May/June 2020). The mark or mark type is shown in brackets.
- Value of L in the range 0.987–0.993 m.
- Value of y₁ > y₂.
- Correct calculation of y.
- Five sets of readings of m and y (different values) showing the correct trend and without help from the Supervisor scores 5 marks, four sets scores 4 marks etc.
- Range: Must include values of m ≤ 100 g and m ≥ 140 g.
- Column headings: Each column heading must contain a quantity, a unit and a separating mark where appropriate. The presentation of the quantity and unit must conform to accepted scientific convention e.g. y / cm.
- Consistency: All raw values of y₁ and y2 must be given to the nearest mm only.
- Axes: Sensible scales must be used, no awkward scales (e.g. 3:10). 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.
- 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.
- Quality: All observations in the table (at least 4) must be plotted on the grid. Trend of points on graph must be correct. It must be possible to draw a straight line that is within ±2.0 cm (to scale) on the y/ cm axis (normally y-axis) of all plotted points.
- Line of best fit: Judge by balance of all points on the grid about the candidate's line (at least 4 points). There must be an even distribution of points either side of the line along the full length. If there are 5 or more points, allow one anomalous point only if clearly indicated by the candidate. Line must not be kinked or thicker than half a small square.
- Gradient: The hypotenuse of the triangle used must be greater than half the length of the drawn line. The method of calculation must be correct. Do not allow Δx / Δy. Both read-offs must be accurate to half a small square in both the x and y directions.
- y-intercept: Correct read-off from a point on the line and substituted into y = mx + c. Read-off must be accurate to half a small square in both x and y directions. or Intercept read directly from the graph with read-off at x = 0 accurate to half a small square.
- Value of A = candidate's gradient and value of B = candidate's intercept. The values must not be fractions.
- Units for A (e.g. cm g⁻¹) and B (m, cm or mm) correct.
- Calculation of R correct [= 2(L – B) / A] and given to three significant figures.
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