May June 2004 Complete Work Solution with Examiner Report 9702_s04_qp_2.

1 (a) State the difference between a scalar quantity and a vector quantity.

scalar: magnitude only

 vector: magnitude and direction (allow scalar with direction)
 [2] (allow 1 mark for scalar has no direction, vector has direction)

Examiner report : 
Almost all candidates stated satisfactorily the difference between scalar and vector quantities.
Candidates should be encouraged to use correct terminology. For example, ‘magnitude’ rather
than ‘size’ or ‘value



Q2) (b) Two forces of magnitude 6.0 N and 8.0 N act at a point P. Both forces act away from point P and the angle between them is 40°. Fig. 1.1 shows two lines at an angle of 40° to one another.

Most candidates did construct a parallelogram or a triangle with directional arrows on the vectors.
There were some very good, accurately drawn figures but many wrongly assumed that the lengths
of the given dotted lines were appropriate for the sides of the parallelogram or triangle. They then
gave the answer as the length of the ‘resultant’, without any regard for scale. A significant number
calculated the resultant, having drawn an appropriate diagram. Others, however, disregarded the
instruction and calculated the resultant, without drawing even a sketch diagram


2 Fig. 2.1 shows the variation with distance x along a wave of its displacement d at a particular time.

The wave is a progressive wave having a speed of 330 m s–1. (a) (i) Use Fig. 2.1 to determine the wavelength of the wave. wavelength = ................................... m


λ = 0.6 m

With few exceptions, candidates read correctly the wavelength from the graph and completed the

calculation to obtain the frequency.

(ii) Hence calculate the frequency of the wave. frequency = .................................... Hz [3]


frequency (= v/ λ )
                = 330/0.60 = 550 Hz


[3] (use of c = 3 x 108 ms-1 scores no marks)


(b) A second wave has the same frequency and speed as the wave shown in Fig. 2.1 but has double the intensity. The phase difference between the two waves is 180°. On the axes of Fig. 2.1, sketch a graph to show the variation with distance x of the displacement d of this second wave. [2]


As 


We can write it as: 
Where  is just a random constant (and so doesn't affect by how many times intensity increases/decreases as it remains the same)

So for when amplitude increases by for example 2 times, then yes intensity increases by 4 times

You could then in a way rewrite the equation as:



Where  is another random constant

And hence 

So the amount of times intensity is increased by, amplitude is increases by the square root of that factor.
eg Intensity increases by 2 times, amplitude increased by