A student is determining the weight of a uniform metre rule using a balancing method.
She places a load P=3.0 NP = 3.0\text{ N}P=3.0 N at the 80.0 cm mark and balances the rule on a pivot.
The rule balances when the pivot is placed at the 72.0 cm mark.
Calculate the actual distance X X\,X from the 80.0 cm mark to the pivot. X=X = X= ...................................................\text{...................................................}................................................... cm\text{cm}cm
Calculate the actual distance Y Y\,Y from the pivot to the centre of the rule (the 50.0 cm mark). Y=Y = Y= ...................................................\text{...................................................}................................................... cm\text{cm}cm
Determine a value W1 W_1\,W1 for the weight of the metre rule using the equation:
W1=P⋅XY W_1 = \frac{P \cdot X}{Y} W1=YP⋅XW1=W_1 = W1= ...................................................\text{...................................................}................................................... N\text{N}N
The student keeps the pivot at the 72.0 cm mark and moves the load P P\,P to the 85.0 cm mark. She places a second load Q Q\,Q of weight Q=1.5 NQ = 1.5\text{ N}Q=1.5 N on the metre rule and adjusts its position so that the rule balances. State whether the load Q Q\,Q must be placed to the left (towards the 0.0 cm mark) or to the right (towards the 100.0 cm mark) of the pivot. Explain your answer without a detailed calculation.
The student uses the values of P P\,P and Q Q\,Q and their distances from the pivot to calculate a second value W2 W_2\,W2 for the weight of the rule:
W2=1.15 N W_2 = 1.15\text{ N} W2=1.15 NThe student expects W1 W_1\,W1 and W2 W_2\,W2 to be equal. State whether the results support this expectation. Justify your answer by reference to your calculated W1 W_1\,W1 and the given W2W_2W2.
Suggest one practical reason why it is difficult to obtain exact results with this balancing experiment.
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.