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 Physics Paper 1, MAy/June. 2009
 Questions: 1 2 3 4 5 6 Main

Weakness/Remedies
Strength

Question 4

(a)  Diagram

You are provided with two metre rules, two knife edges, optical pin, a known mass and other necessary apparatus.

1. Affix the optical pin at the 50 cm mark of one of the meter rules supplied, with a sellotape/plasticine.
2. Place the rule horizontally on the knife edges such that the knife edges are at the 17.5 cm and 82.5 cm marks.  Record the distance D between the knife edges.
3.  Mount the other metre rule vertically with the retort stand and clamp and place it close to the pin to measure the depressions of the metre rule when the weight M is suspended at its mid point.
4. Read and record the position h0 of the pointer on the vertically mounted metre rule, with no weight suspended on the horizontal metre rule.
5. Suspend M at the midpoint of the metre rule.
6. Read and record the new position of the pointer h1.
7. Determine the depression of the metre rule H =h1  -h0.  Evaluate log H and Log D.
8. Repeat the procedure with the knife edges set at 20.0 cm and 80.0 cm;  22.5 cm and 77.5 cm and 25.0 cm and 75.0 cm marks.  Each time read and record the distance D and h1.
1. Evaluate the depressions H in each case and log H and log D.  Tabulate your readings.
2. Plot a graph of log H on the vertical axis and log D on the horizontal axis.
3. Determine the slope, s, of the graph.
4. State two precautions taken to ensure accurate results.

(b)   (i)     Define moment of a force about a point.

An object of mass 60 g is suspended at the 16 cm mark of a uniform metre rule.  The metre rule is adjusted on a pivot until it balances horizontally at the 38 cm mark.

Determine the mass of the metre rule.

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Observation

This question was well attempted by many candidates.  However, few candidates did not record their observation to the required number of decimal places and in the evaluation of logarithms of numbers and this affected their graphs.  Precautions were often not stated in acceptable language that is reported speech.

Part (b) was fairly attempted by most responding candidates.

In part (a) candidates were expected to:

1.read and record to 1 decimal place values of h0, D and also determine correctly four values of H = (h1h0);

(Trend: as D decreases, H also decreases)

2. evaluate correctly to at least 3 decimal places four values of log H and log D each;

3. record data in a composite table showing D, h1, H log  and log D;

4.distinguish the graph axes, select reasonable scales, plot four points correctly and draw a line that best fits the points;

5.draw a large right angled triangle on the graph line in order to determine the slope, s;

6. read ∆log H and ∆log D and also evaluate     ∆log H
∆ Log D

1. state any two of the following precautions in acceptable form of speech.
2. Avoided parallax error in reading of the metre rule
3. Avoided draught
4. Ensured reading is repeated (shown on the table)
5. Ensured firm clamping of the vertical metre rule

(b)(i)    Definition:

Moment of a force about a point is the product of the force and the perpendicular
distance of its line of action from the point.

(ii)      Determination of the mass of metre rule

0 cm        16cm            38cm        50cm                                              100cm

60g.                                              m

Using the principle of moment

m (50 – 38) = 60(38 -16)
12  = 60 x 22

m   =   110g.