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Physics Paper 1, MAy/June. 2008  
Questions: 1 2 3 4 5 6 Main

General Comments

Question 4

You are provided with a uniform metre rule, a knife edge, some masses and other necessary apparatus.

(i)         Determine and record the centre of gravity of the metre rule.

(ii)        Fix the 100 g mass marked N at a point Y, the 80 cm mark of the rule using an adhesive.

(iii)       Suspend another 100 g mass marked M at X, a distance A = 10 cm from the 0 cm mark of the rule.   

(iv)      Balance the arrangement horizontally on the knife edge as shown in the diagram above.   

(v)        Measure and record the distance B of the knife edge from the 0 cm mark of the rule.           

(vi)       Repeat the procedure for four other values of A =  15, 20, 25, and 30 cm.

(vii)      Measure and record the corresponding values of B in each case.  Tabulate your  readings.

(viii)      Plot a graph of B on the vertical axis against A on the horizontal axis.

(ix)     Determine the slope, s, of the graph.  Also determine the intercept, c, on the vertical axis. 

(x)       Evaluate (A)   =    k1  =   1 – 2s   100; 
                         (B)   =    k2  =   2c   160. 
 (xi)      State two precautions taken to obtain accurate results.                           [21 marks]

(b) (i)   Define moment of a force about a point.                                                    [2 marks]

    (ii)   State two conditions under which a rigid body at rest remains in equilibrium when acted upon by three non-parallel coplanar forces                                       [2 marks]


The candidates were required to:

(i) set up an experiment as shown in the diagram above:

(ii) measure and record G as well as five values of B in cm to at least 1 decimal place in trend.
(Trend: As A increases, B decreases)
(iii) measure and record five values of A in cm.

(iv) record data on composite and complete table showing A and B.

(v) indicate the graph axes; select reasonable scales, plot the five points correctly and draw a line that best fits the point;

(vi) draw a large right angled triangle on the graph line.

(vii) read ΔA and ΔB and also evaluate ΔA

(viii) show intercept on the vertical axis; read and record its value;
(ix) correctly evaluate k1 and k2;

(x) state any two of the following precautions in acceptable form of speech:
- draught was avoided
- ensure mass did not rest on the table
- avoided error due to parallax when reading metre rule;
- repeated readings (shown on table)
- zero error of metre rule noted and corrected for.

(b) (i) The moment of force about a point is defined as the product of the force and its perpendicular distance from the point to the line of action of the force.

(ii) The conditions under which a rigid body remains in equilibrium when
acted upon by three non- parallel coplanar forces are:

I. there is no rotation under the action of the forces
II. the forces must be concurrent (i.e. they must meet at a point)
III. the resultant of the forces must be equal to zero
IV. the algebraic sum of the resolved components of the forces is zero.

This question was generally well attempted by candidates. Evaluation from graph work was poorly done. Evaluation of k1 and k2 was wrongly done by most candidates.
The b part was well attempted.

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