Physics Paper 3, May-June 2015

Question 1A

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You are provided with a retort stand, boss head, clamp, stop watch slotted weights, hanger, grooved pulley, thread, measuring tape and other necessary materials

(i) Measure and record the radius R of the pulley.

(ii) Set-up the apparatus as illustrated in the diagram above, such

that the clamp is 1.5 m above the floor.

(iii) Tie one end of the thread to the pulley.

(iv) Tie the other end of the thread to the hanger.

(v) Slot a mass m = 50 g on the hanger.

(vi) Wind the thread around the groove of the pulley until the base of

the hanger is at a height h = 1.4 m above the floor.

Maintain this height h for every other value of m throughout the experiment.

(vii)Release the mass to unwind the thread

(viii) Determine and record the time t taken by the mass m to reach the floor.

(ix) Evaluate t2

(x) Also evaluate a = , T = (10 – ) and =

(xi) Repeat the procedure for four other values of m = 70 g,90 g,110 g and 130 g.

(xii) Tabulate your reading

(xiii) Plot a graph with Cl on the vertical axis and T on the horizontal
axis .

(xiv) Determine the slope s, of the graph
(xv) Evaluate I =

(xvi)        State two precautions taken to obtain accurate results
                                                                                             [ 21 marks]

(b) (i)   Define centripetal force                                      [2 marks]

(ii) An object drops to the ground from a height of 2.0 m, calculate the speed with
which it strikes the ground

[ g = 10ms-2 ] [ 2 marks ]

Observation

    Part (a) this question was not popular among the candidates. Candidates are challenged in
    measuring the time of fall of the weight. Most responding candidates failed to record the
    value of R as demanded in the question. Few recorded the radius as 6m! Some had problem
    in evaluating T = ( 10 – a)   However, the graph and slope were well attempted .
The precautions were well stated.
    Part (b) many candidates failed to do justice to this part. Performance was poor.

    Candidates were expected to

Measure and record Radius of pulley R to at least 1 d. p. in cm

Record five values of m in grams

Measure and record five values of t to at least 1 d.p in seconds and in t

trend: as m increases t decreases

Evaluated five values of t2 to at least 2 d. p.

Evaluated five values of a =

Evaluated five values of T =

( 10 – a)

Evaluated five values of

Composite table m, t, t2, a,T and

in distinguished both axes

Plot graph using reasonable scales

Draw line of best fit

Evaluate the slope as I =

State any two of the following precautions

Retort stand / pulley firmly clamped

Avoided parallax error in reading stop-watch/clock/metre rule/ tape rule

Noted / corrected zero error on stop watch/ clock/metre rule / tape rule

Repeated readings shown on table.

The expected answers for part (b) are:

        b(i)     Centripetal force is the inward force / force acting towards the centre of the circle
required to keep an object moving with a constant speed in a circular path                                       OR
F =                        Where the symbols have their usual meanings

(ii)             v2 = u22gh                OR                   k.E. = P.E.
v2 =02 + 2 x 10 x 2                                  ½ mv2 = mgh
= 40                                                              v2 = 2 x 10 x 2
v =                                                         v = 6.32 ms-1
=   6.32 ms-1

Physics Paper 3 WASSCE (SC), 2016

Question 1A

Observation