Alternative A
Question 1A
A known mass M is used to depress a metre rule placed on two knife edges as illustrated in the diagram above.
A vertically clamped rule with the aid of an optical pin fixed to the horizontal rule is used to note the initial pointer reading ho before the M is placed on the rule and hi after suspending M.
The separation D between the knife edges is also noted and maintained throughout the experiment.
The procedure is repeated four other values of M and the depression H in each case is measured and recorded.
Fig. 1(a) shows the various masses Mi
Fig 1(b) shows the positions of pin hi where i = 0, 1, 2, 3, 4 and 5.
- Read and record the masses Mi.
- Measure and record the values of hi.
- Determine H = (hi – ho)
- Tabulate your readings.
- Determine the mean Q of Li.
- Plot a graph of H on the vertical axis and M on the horizontal axis.
- Determine the slope s, of the graph.
- State two precautions that are necessary to ensure accurate results when performing this experiment
(b) (i) State two examples of objects in stable equilibrium.
(ii) A rod of negligible mass is balanced horizontally by two weights 10 N and 15 N placed 30 cm and y cm respectively from a pivot. Calculate the value of y
Observation
Part (a) Candidates performance was below average. However, many candidates could not interpret the data given correctly thereby making it difficult to obtain the correct converted value.
Part (b) The question was fairly attempted. Many candidates had difficulty in identifying the forces acting on the metre rule. However, the examples of objects in stable equilibrium was well attempted.
The expected response:
- Value of ho measured and recorded to at least 1 d.p. and
within tolerance of ± 0.1 cm
- Value of ho correctly converted
- Value of hoReal (27 + hoConv ) correctly evaluated
- Five values of M recorded in grammes
- Five values of hi measured and recorded to at least 1 d.p and
within tolerance of ± 0.1 cm
- Five values of hi correctly converted
- Five values of hiReal (27 + hiConv ) correctly evaluated
- Five values of H = (hiReal – hoReal) correctly evaluated
- Composite table showing at least M, hi and H
- Plot a graph using reasonable scales
- draw line of best it
- determine the slope of the graph
- state any two of the following precautions.
e.g.
- Ensured knife edges are firm
- Avoided parallax error on metre rule
- Noted/note zero error on metre rule
- Ensured that second metre rule is vertical/erect
- Avoided draught
In part b, the expected answers are:
b(i) Object in Stable Equilibrium
e.g
- a cone resting on its base
- a racing car (with low centre of gravity/ wide base)
- a ball or sphere in the middle of hemispherical bowl
- a Bunsen burner on its base
- an inverted funnel
- chair/table on its four legs
- inverted table
