Question 1
A metre rule is balance horizontally on a knife edge and its centre of gravity, G is noted. A body labeled R is fixed securely at G means of a piece of string. A mass, m is attached securely at P which coincides with the 5 cm mark of the metre rule. The position of P is kept constant throughout the experiment.
The loaded metre rule is balanced horizontally on the knife edge at K and the distance
x = PK is measured. The procedure is repeated for four other values of M.
Fig I (a) illustrates the position of G relative to the 0 cm mark of the metre rule.
Fig I (b) illustrate the masses m, and Fig 1 (c) illustrate xi where i= 1,2,3,4 and 5
- Measure and record the raw value, Go of the centre of gravity of the metre rule.
- Use the given scale to convert Go to real value G.
- Read and record Mi
- Measure and record the raw distance xi
- use the given scale to convert xi to real value Xi
- evaluate X-1
- Tabulate the results
- Plot a graph with X-1 on the vertical axis and M on the horizontal axis.
- Determine the slope, s, of the graph
- If ,calculate Mg
- State two precautions that are necessary to obtain accurate results when performing this experiment.
(b) (i) State two conditions under which a body would be stable.
(ii) State two factors that determine the magnitude of the moment about a point.
Observation
Part (a) Candidates performance was below
average. Most candidates were able to measure the raw values but failed to find the converted which leads to gross error.
Part (b) The question was fairly attempted. Many candidates failed to state conditions under which a body would be stable and factors determining the moment about a point.
The expected response is as stated below:
- Raw value of G0, correctly measured and recordedto at least 1 d.p.
- and within tolerance of ± 0.1 cm.
- Value of G correctly converted
- Five values of M correctly read and recorded in g.
- Five values of x correctly measured and recorded to at least 1 d.p.
- and within tolerance of ±0.1 cm
- Five values of X correctly converted
- Five values of X-1 correctly evaluated to at least 3 d.p.
- Composite table showing at least M, x, X and X-1.
- Plot a graph using reasonable scales
- Draw line of best it
- Determine the slope of the graph
- Evaluate s =
- state any two of the following precautions.
e.g.
- Avoid parallax error in reading metre rule / weighing balance
- Avoid draught
- Note zero error on weighing balance/metre rule
- Repeated readings stated
(b) (i) Conditions under which a body can be stable
- Wide/broad base
- Low centre of gravity
(ii) Factors that determine the magnitude of moment about a point
- magnitude of applied force
- perpendicular distance between the point of application of the
force and the turning point/pivot/fulcrum