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 Physics Paper 2, Nov/Dec. 2013
 Questions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Main
Weakness/Remedies
Strength

Question 11

Question 11

1.     List three facts about the acceleration of a free falling object due to gravity.

.

1.     List two objects each which may be considered as projectiles in:
2.  Sports;
3. Warfare.
4.   A ball of mass 120g was projected vertically upward from the earth surface with a speed of 25 ms-1.  The height of the ball was determined at regular intervals as shown in the table below.
 Height  H/m Time t/s 11.25 20.00 26.25 30.00 31.25 0.5 1.0 1.5 2.0 2.5
1. Plot a graph with height, H on the vertical axis and time, t on the horizontal axis starting both axes from the origin (0,0).

[draw a smooth curve through the points]

1. Using the graph, determine the height of the ball at t  =  1.7s.
1.    The combined mass of a bicycle and its rider is 60 kg.  Calculate the magnitude

of the forward force produced by the bicycle if its speed increases from 10 ms-1 to
15  ms-1 in 3.0 s.
[Neglect friction and air resistance]

_____________________________________________________________________________________________________

Part (a).  This question was very popular among the candidates and it was fairly well    attempted.  However, some candidates could not correctly list all the three facts.  Few of the candidates  mixed up their answers with centre of gravity.
Part (b)  many candidates only listed the object without the action word (verb) to give           it the projectile sense  e.g discuss instead of discuss thrown.  Most candidates did not
know that the object becomes a projectile only when it is in motion (action).

Part (c).  Performance was below average as many candidates plotted the points but
did not start it from the origin as required in the question.  Many even drew a straight
line to join the points instead of a smooth curve.

Part (d).  Most candidates answered this part correctly.  Performance was above
average.

1. Acceleration of free fall due to gravity

e.g  -  its magnitude reduces with altitude (height)
-   at equator, its value is about 10ms-2
-   its value on earth is about 6 times that on  the moon/
greater than  that on the moon)
-   It is a vector quantity.
(b)   Objects considered as projectiles
In Sports                                                                   In Warfare
e.g  - Discuss thrown                                         e.g. Missiles fired/thrown
-  Short-put projected                                   -  Bullets fired
-   Javelin projected                                      -   Arrow shot/thrown
-   Golf ball hit.
-    kicked football into the air

I)    Axes correctly distinguished                                                                         (II)  Reasonable scales (Both axes)                                                                    (III)  Five points correctly plotted                                                                       (IV)  Curve of best fit

(ii)   H correctly shown on graph
Correctly recorded
(d)    v  =  u + at
15  =  10  + a x 3
a   =     = 1.67 ms-2
F  =  ma
=   60 x 1.67
=  100N