Physics Paper 3, Nov/Dec 2010
 Questions: 1 2 3 Main
Weakness/Remedies
Strength

Question 1

(a)    Diagram

The diagram above illustrates a uniform metre rule which is initially mounted horizontally and symmetrically on two knife edges, L em apart with the graduated side facing upwards. When a mass M is hung at the mid-point of the rule, it depresses it by a distance, d, which is measured on a vertical scale.

The initial pointer position Yo, is read and the final pointer Yi after the load M has been suspended is read and recorded. The procedure is repeated for four other values of L.
Fig. 1(a) shows the initial pointer position Yo and the final position Yi
where i = 1, 2, 4, and 5.
Fig. 1(b) represents the corresponding distances of separation L, between the knife edges A and B where i = 1,2,4, and 5.
(i)            Read and record the initial pointer position Yo and the final pointer position Yi.
(ii)           Measure and record the corresponding values of Li•
(iii)         Evaluate d = (Yi - Yo) and L3 in each case.

(v) Plot a graph of d on the vertical axis against e on the horizontal axis.
(vi) Determine the slope, s, of the graph.
2.5 x 10-13
(vii) Evaluate y =          s
(viii) State two precautions that are necessary to ensure accurate results when performing this experiment.
(b)(i) State the conditions under which a number of parallel coplanar forces will be in equilibrium.

(ii)

In the diagram above, the point G is the centre of gravity. Calculate the tension T2

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Observation

This question was popular and fairly attempted by many candidates. Some of the candidates used raw value ofL to evaluate L3 and also to plot their graphs instead of the converted values of L. Some ofthe candidates that converted had difficulties plotting with the large values of L 3 arrived at.

Many candidates could not state satisfactory precautions relevant to this experiment. The (b) part was fairly tackled. However, some candidates omitted the phrase "about a point" in the statements of conditions of parallel coplanar forces in equilibrium.

The demands of part (a) include the following:

- Read and record Yo. Yi and L, to at least 1 d.p;
- Evaluate five values ofL3 and d (Yi - Yo) in each case;
- The graph axes should be distinguished and reasonable scales selected;
- Plot graph of d against e and the slope evaluated;
- Stating the precaution to ensure accurate results as follows:
- avoid parallax error when reading the metre rule;
- note and correct for zero error on metre rule;
- ensure that the mass does not touch the table/the vertical scale;

The expected answers to part (b) are as follows:

(b)(i) (A)The sum of the forces in one direction is equal to the sum of the forces in the opposite direction.

(B)           The sum of the clockwise moments about a point is equal to the sum of the anti clockwise moments about the same point.

(ii) T, + T2 = 120
50 + T2 = 120
T2 = 70N