From Fig. 3.2, find the distance $d$ from the pivot to the centre of the $20\,\text{g}$ mass when the metre rule is as nearly balanced as possible.
Describe the method the student uses to balance the metre rule with the $20\,\text{g}$ mass.
Transfer your value of $d$ for mass $m = 20\,\text{g}$ in (a)(i) to Table 3.1. Work out $\frac{1}{d}$ for each mass $m$, and enter every value in Table 3.1. State your answers to an appropriate number of significant figures.
Suggest why no value of $d$ can be obtained for mass $m = 10\,\text{g}$.
On the grid in Fig. 3.3, plot $\frac{1}{d}$ on the $y$-axis against $m$ on the $x$-axis. Begin both axes at the origin $(0,0)$. Draw the straight line of best fit.
Calculate the gradient $G$ of your line. Show all your working, and mark on the graph the values you use.
The mass $M$ of the metre rule can be found from $M = 160 - \frac{0.040}{G}$. Use your value of $G$ to work out $M$.
From your graph in Fig. 3.3, determine the mass of the piece of modelling clay when the metre rule is balanced with the modelling clay $40.0\,\text{cm}$ from the pivot. Show your working.