Physics Paper 2, Nov/Dec. 2011
 Questions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Main
Weakness/Remedies
Strength

Question 11

(a)     (i)  Explain relative motion.

(ii)  Two cars moving in opposite directions on the same straight road with velocities 80 km
h-1 and 60 km h-1 respectively pass each other at a point.  Determine the velocity of
the first car relative to the second.

(b)     (i)   Define force

(ii)   Classify the following forces as either contact forces or field forces; push; tension;
gravitational; electrostatic; reaction and magnetic.

(c)      A body starts from rest and travels in a straight line for 2 seconds with uniform
acceleration of 1 ms-2.  It then travels at a constant speed for some time before coming
to rest with a uniform retardation of 2 ms-2.  The total distance covered by it is 1.5m

(i) Draw and label a velocity – time graph for the motion.
(ii)  Calculate the:
(A)  velocity attained after the first 2 seconds;
(B)   total time taken for the journey.

Part(b) many candidates were unable to explain relative motion.  Those that made effort lost marks because they did not mention the frame of reference in their explanation.  Performance was average.

Part(b) majority of the responding candidates were able to define correctly force and classify the given forces as  either contact forces or field forces.

Part(c) the drawing of the velocity –time graph did not pose any problem to the candidates; however, majority of those that attempted this question failed to calculate correctly the total time taken for the journey by the body.

_____________________________________________________________________________________________________

a)(i)   This is a change in position measured from a point or frame of reference which may
be stationary or moving e.g.
-      movement of a person walking inside a moving train
-      a person inside a moving train observing a stationery observer/tree outside the
train .

(ii)        Relative velocity  =  V = Vfirst – V second
=  80 – (-60)
= 140 kmh -1

(b)(i)    Force is an agent that changes or tends to change the state of rest or of uniform
motion in a straight line of a body.

 Contact forces Field forces Push Tension Reaction Gravitational force Electrostatic force Magnetic force.

(c)   V/ms-1

Axes correctly distinguished
origin indicated (020)

(ii)   (A)   Acceleration  a   =   V/t1

V  =  at1
=  1  x  2
=   2ms-1

Retardation a1  =  V/t3
t3  =  V/a1       =   2/2
=  Is
x  =   area of trapezium

15   =   ½  (t2 + t2 + 3) 2
=  2t2  +  3
t2  =  6s

Total time required  =  6  + 3 = 9s