Physics Paper 2, May/June. 2011

Questions:	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	Main

General Comments
Weakness/Remedies
Strength

Question 11

What is a vector quantity?
Three vectors 3 ms-1 N 45o W, 12 ms-1W and 5ms-1 S act at a point.
Sketch a vector diagram to illustrate the given information
Calculate the resultant of the vectors.
In a laboratory experiment to determine the force constant of a spiral spring, the mass on the spring was varied and the corresponding extensions were measured and recorded as shown in the table below.

Mass m/g	Weight W/N	Extension e/cm
50 100 150 200 250		6.5 11.0 15.0 20.0 25.0

Copy and complete the table. (Take g = 10ms-2 )
Plot a graph with weight, W, on the vertical axis and extension, e, on the horizontal axis.
Using the graph, determine the force constant of the spring.
Determine the natural length of the spring if its length was 38.0 cm when loaded with 250 g mass.

Observation

Part (a) the definition of a vector quantity posed no problem to most candidates. Performance was high.

Part (b), candidates failed to put down a correct sketch of the vector diagram as a result of not indicating directions or using reasonable relative lengths to represent magnitudes. The resultant vector sort could not be determined due to inability to put down a correct sketch. The direction of the resultant vector was not determined by few candidates that were able to determine the resultant vector magnitude correctly.

Part (c), many candidates could not plot the graph correctly. Scales were wrongly chosen, points were wrongly plotted and line of best fit could not be drawn. The natural length of the spring sorted for could not be determined. Generally, performance was fair.

The expected answers are

A vector quantity is (a physical) quantity that has both magnitude and direction

$Description: C:\Documents and Settings\Administrator\My Documents\SC DOC\scan0041.tif$

Sketch of vector diagram correctly showing and labeling relative length of arrows angles 45o and 90o

                  Tan θ = 2.879   = 0.2039
                          14.121
                     θ = 11.50
                     R = 14.4ms-1 S78.5oW

Mass m/g	Weight W/N	Extension e/cm
50 100 150 200 250	0.5 1.0 1.5 2.0 2.5	6.5 11.0 15.0 20.0 25.0

$Description: C:\Documents and Settings\Administrator\My Documents\SC DOC\scan0042.tif$

Both axes correctly distinguished

Reasonable scales (both axes)
Five points correctly plotted
Line of best fit

    Force constant = slope = DW
                  De
                                    DW   correctly evaluated
                                   De
  Natural length = 38.0 – 25.0
=   13.0 cm