KNEC KCSE Physics Paper 3 Question Paper / 2016 KASSU JET JOINT EXAMINATION

Part A
You are provided with the following
• A metre rule
• Knife edge raising 20cm above bench
• One 50g mass and one 100g mass
• Some thread
• Some water in a beaker
• Liquid L in a beaker
• Tissue paper
Proceed as follows:
a) Balance the meter rule on the knife edge and record the reading at this point.
Balance point = ………………………………m (1mk)

For the rest of this experiment the knife edge must be placed at this position.
b) Set up the apparatus as shown in figure below. Use the thread provided to hang the masses such
that the positions of support can be adjusted.

The balance is attained by adjusting the position of the 100g mass. Note that the distance x and d
are measured from the knife edge and the 50 mass is fully submerged in the water. Record the
values of x and d.
i) x1 = ………………………………………………….cm (1mk)
d = …………………………………………………..cm (1mk)
ii) Determine W1 (weight of the object in water) (2mks)
iii) Determine the upthrust Uw in water of the 50g in water (1mk)
c) Now balance the metre rule when the 50g mass is fully submerged in the liquid L.
x2 =…………………………………………cm (1mk)
Apply the principle of moments to determine the weight W₂ of 50g mass in the liquid L and
hence determine the upthrust U_L in the liquid.
W₂ (2mks)
U_L (1mk)
d) Determine the relative density R.D of the liquid L, given that
R.D =U_L/U_w (1mk)

Part B
You are provided with the following
• A rectangular glass block
• Four optical pins
• A piece of soft board
• A plain sheet of paper
• Cellotape
You are also required to have your complete mathematical set.
Proceed as follows:
a) Place the plain sheet of paper on the soft board and fix it using the cellotape provided. Place the
glass block at the centre of the sheet, and draw its outline. Remove the glass block. See the figure
below

Draw a normal at a point 2cm from the end of the longer side of the block outline. This normal
line will be used for the rest of the experiment.
b) By viewing through the glass from the opposite side stick two other pins P₃ and P₄ vertically such
that they are in line with the images of the first two pins. Draw a line through the marks made by
P₃ and P₄ to touch the outline.
Measure and record in the table below the perpendicular distance d between the extended line and
the line, P₃P₄. See figure above.
c) Record this value in the table below and repeat the process for other angles shown in the table.
NB: The sheet of paper with the drawing must be handed in together with this question paper.
Ensure you write your name and index on the sheet paper.

(3mks)

f(i) On the grid provided, plot a graph of d (y –axis) against ϴ (5mks)

(ii) Using the graph, estimate the value of d when ϴ = 0^o(2mks)