A student determines the weight of a metre rule. She uses an apparatus where the metre rule is supported by a pivot at the 20.0 cm\mathbf{20.0\text{ cm}}20.0 cm mark and is suspended from a vertical forcemeter by a loop of thread at the 80.0 cm\mathbf{80.0\text{ cm}}80.0 cm mark.
The student places a 3.0 N cylindrical weight on the metre rule. Looking from above, she observes that the left-hand edge of the weight aligns with the 33.5 cm mark and the right-hand edge aligns with the 36.5 cm mark on the rule. Calculate the position of the center of this weight and hence find its distance l l\,l from the pivot. Show your working clearly.
She then adjusts the height of the suspension so that the rule is horizontal, and reads the force F F\,F on the forcemeter. The vertical scale on the forcemeter has major markings every 1.0 N (from 0.0 N to 5.0 N) with 10 small subdivisions between each Newton. The indicator line level is at 6 small divisions below the 1.0 N mark (towards 2.0 N). Read and state the value of the force F F\,F shown on the forcemeter.
Explain how the student ensures that the rule is horizontal before taking the reading.
The student repeats the procedure for different values of lll. Her readings are shown in the table:
| l (cm)l \text{ (cm)}l (cm) | F (N)F \text{ (N)}F (N) |
|---|---|
| 15.0 | 1.60 |
| 25.0 | 2.10 |
| 35.0 | 2.60 |
| 45.0 | 3.10 |
| 55.0 | 3.60 |
Describe the key steps to plot a graph of F / NF\text{ / N}F / N (y-axis) against l / cml\text{ / cm}l / cm (x-axis), starting both axes from the origin (0,0)(0,0)(0,0).
From the linear relationship in the table or a plotted line of best fit, determine F0F_0F0, the value of F F\,F when l=0l = 0l=0.
Calculate the weight WRW_{\text{R}}WR of the metre rule using the equation:
WR=2×F0 W_{\text{R}} = 2 \times F_0 WR=2×F0A student carrying out this experiment finds it difficult to be sure that the center of the weight is placed at the correct value of lll. Suggest a more precise method of applying the load to the metre rule in this experiment, and explain why this method is an improvement.
43 exam-style questions on CIE IGCSE Physics 1.5.2a Moment of a force. Each one has a worked solution and a mark scheme showing where the marks go.