Question 111 marks
Question
In this experiment, you will determine the mass MR of a metre ruler using a balancing method. Carry out the following instructions, referring to Fig. 1.1. load a b metre ruler bench 5.0 cm mark pivot 50.0 cm mark Fig. 1.1 (a) (i) Place a load of mass M = 20 g with its centre at the 5.0 cm mark of the metre ruler. Explain briefly how you make sure that the centre of the load is at the 5.0 cm mark. You may draw a diagram if it helps your explanation. …… [1] (ii) Place the metre ruler on the pivot. Adjust the position of the metre ruler on the pivot until the metre ruler is as near as possible to being balanced. Check that the position of the centre of the load remains at the 5.0 cm mark. Record, in Table 1.1, the scale reading p on the ruler at the position of the pivot. Calculate, and record in Table 1.1: • The distance a between the 5.0 cm mark and the pivot. Use your value of p and the equation a = p – 5.0. • The distance b between the 50.0 cm mark and the pivot. Use your value of p and the equation b = 50.0 – p. Repeat this procedure for values of M = 40 g, 60 g, 80 g and 100 g. [2] Table 1.1 b M/g p / cm a / cm b / cm a 20 40 60 80 100 b (b) For each value of M, calculate and record in Table 1.1 the value . [1] a b (c) Plot a graph of M / g (y-axis) against (x-axis). a Draw the best-fit line. [4] (d) (i) Determine the gradient G of the graph. Show clearly on the graph how you obtained the necessary information. G = …… [1] (ii) The mass MR of the metre ruler is numerically equal to G. Write down the value of MR in this experiment. Include the unit. MR = …… [1] (e) The determination of MR by this method assumes that the centre of mass of the metre ruler is at the 50.0 cm mark. A student finds that the centre of mass of his metre ruler is at the 48.7 cm mark. Suggest how he changes the procedure in (a)(ii) to allow for this. …… [1] [Total: 11]
Mark scheme
1(a)(i) take scale reading at left- and right-hand side of mass and ensure average is 5.0 cm / owtte 1 1(a)(ii) 5 readings of p < 50.0cm, all decreasing 1 a + b = 45.0 cm 1 1(b) correct calculations of b / a to 2 or more decimal places 1 1(c) graph: 1 axes labelled with quantity and unit appropriate scales (plots occupying at least ½ grid between plotted points) 1 plots all correct to ½ small square and precise plots 1 well-judged line and thin line 1 1(d)(i) G present and triangle method seen on graph 1 1(d)(ii) MR in range 100 to 200 and with unit of g 1 1(e) b calculated from b = 48.7 − p 1