Physics Paper 3, Nov/Dec 2011
 Questions: 1 2 3 Main
Weakness/Remedies
Strength

Question 1

The internal diameter, D, of an empty beaker is measured.

Water is then poured into the beaker until it is about two-thirds full.  The depth, do, of the
water in the beaker is measured using a graduated scale fixed to the beaker.

A body of mass, M, supported on the free end of a piece of thread, fixed to the boss of a
retort stand, is immersed completely in the water as shown in the diagram above.  The
new depth, d, of the water in the beaker is measured and recorded.

The procedure is repeated with four different masses.

Fig 1(a), fig 1(b) and Fig 1(c) show the masses M, the diameter, D, of the beaker and
depth, d, of water in the beaker respectively.

(i)     Measure and record the masses, M.
(ii)    Measure and record the corresponding depth d, where  = 1,2,3,4 and 5.
(iii)   Also measure and  record D.
(iv)    Evaluate d – do in each case.
(vi)    Plot a graph with Mi on the vertical axis and (d – d) on the horizontal axis.
(vii)    Determine the slope, s, of the graph
(viii)     Evaluate  K  =     Take p =
(ix)       State two precaution that are necessary to ensure accurate results when performing
this experiment.

(b)  (i)   Show that the relative density of a substance is equal to the weight of the substance
divided by the weight of an equal volume of water

(ii)    The following data were obtained in an experiment

mass of empty relative density bottle                                       =  18.5 g
mass of relative density bottle filled  with water                    =  65.5 g
mass of relative density bottle filled with another liquid  X  =  58.5 g
Use the data to determine the relative density of X.

_____________________________________________________________________________________________________
Observation

This question was answered by almost all the candidates and the performance was quite
good.  The masses M were correctly determined however, the depth do and di were
wrongly measured by almost all the responding candidates because they did not add 2.8 cm
which happens to be the reference point to their measured values.

The graph and slope as well as precautions were well handled by candidates.  Part b(i)
candidates failed to show that the relative density of a substance to be equal to the weight
of the substance divided by the weight of an equal volume of water.  Part b(ii) was poorly
attempted.

Candidates are expected to:

•  measure and record value of D and do.
•  read and record five values of M and d to at least 1 d.p.
• evaluate d-do and record
• plot graph of Mi against (d-do) using reasonable scales
• determine the slope of the graph
• evaluate K =
• state any two of the following precautions.

•   Read water level at the minimum level of the meniscus of water
•   Avoid parallax error in reading metre rule/scale balance
•   Mass not touching the beaker
•   Note/corrected zero error on metre rule/scale balance
•   Ensure metre rule is placed vertically
•   Avoid splashing of water from the beaker
•   Allow the water in the beaker to be still/calm before taking reading.

The expected answers for part  b are:

b(i)    Rd

=   b(i)    Rd     density of substance
density of water
=  mass of substance
mass of equal volume of water

=       mass of substance x acceleration of free fall
mass of equal volume of water x acceleration of free fall

=       weight of substance
weight of equal volume of water

(ii)     Mass of water  =   68.5  -  18.5  =  47g
Mass of liquid  =   58.5  -  18.5   =  40g
Relative density of liquid   =  mass of liquid
mass of equal volume of water
=         40
47
=  0.85