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.
245 exam-style questions on CIE IGCSE Physics 1.5 Forces, covering 1.5.1a Forces, resultant force and motion, 1.5.1b Load–extension graphs and the spring constant, 1.5.1c Friction and drag, 1.5.1d Force, mass and acceleration, 1.5.1e Motion in a circular path, 1.5.2a Moment of a force, 1.5.2b Principle of moments and equilibrium, and 1.5.3 Centre of gravity and stability. Each one has a worked solution and a mark scheme showing where the marks go.