Question 1A

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

 

(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 sellotape.

(iii) Suspend another 50 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 illustrated 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 cm, 20 cm, 25 cm and 30 cm.

(vii) Tabulate your readings.

(viii) Plot a graph with B on the vertical axis and A on the horizontal axis.

(ix) Determine the slope, s, of the graph.

(x) Also determine the intercept, c, on the vertical axis.

(xi) Evaluate:

 

 

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 non-parallel coplanar forces.

 

Part (a) Candidates performance was good. However, many candidates did not record the centre of gravity of the metre rule to at least 1 decimal place and in cm. Also, most candidate started the graph from the origin thereby losing some marks.

 

Part (b) The question was poorly attempted due to candidates’ inability to distinguish between parallel coplanar forces and non-parallel coplanar forces.

 

Candidates were expected to:

- read and record the centre of gravity G correctly to at least 1 d.p in cm

- record correctly five values of A to at least 1 d.p in cm and in trend

- read and record correctly five values of B to at least 1 d.p in cm and in trend

- show composite table containing at least A and B

- Both axes correctly distinguished

- plot a graph using reasonable scales

- draw line of best it

- determine the slope and intercept of the graph

 

evaluate k1 =( (1-2s)/s) x 100, k2 =( 2c/s – 160)

 

- state any two of the following precautions. e.g. e.g.

- Avoided draught

- Ensured mass did not touch/rest on the table

- Avoided error due to parallax on metre rule

- Noted zero error on metre rule

- Repeated readings (shown on table) In part b, the expected answers are: b (i) The moment of a force about a point is defined as the product of the force and perpendicular distance from the point to the line of action of the force. (ii) Conditions of rigid bodies in equilibrium e.g - 1. The resultant of the forces in a given direction must be zero/the algebraic sum of resolved components in a given direction must be zero 2. The algebraic sum of the moments about any point is zero. 3. The forces must be concurrent or meet at a point.