Physics Paper 2, May/June. 2010  
Questions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Main
General Comments
Question 12

(a)Explain the terms:
(i) Inertia;
(ii) Inertia mass.
(b)List three factors which affect the rate of evaporation of water in a pond.
(c)Two ice cubes pressed together for some time were found to stick together when the pressure was removed. Explain this observation
(d)Two vertical capillary tubes of the same diameter are lowered into beakers situated at the same level containing liquids A and B of densities 9.2 x 102 kgm -3 and 1.30 x 103 kgm-3respectively. A suction pump is used to withdraw air from the top of the liquid columns in the tubes by means of aT-piece arrangement until the liquid in a rises to a height of26.0 ern. Calculate the height of the liquid in tube B.
Part (a). Most candidates explained inertia correctly but did not explain inertial mass correctly. Rather they were stating Newton's first law of motion which was not proper.
Part (b). Responses from candidates were satisfactory.
Part (c). Performance was low. Few candidates correctly linked this to regulation but could not explain it as demanded by the question. Some candidates were explaining it in terms of adhesion and cohesion which was wrong.
Part (d). Candidates found this part very tractable.
The expected answers are:
12. (a)(i)Inertia is the reluctance of a body to move if it is at rest or to stop if it is already in motion. The more mass a body has the greater its inertia.
(ii) Inertial mass represents resistance to any type of force whatever the more mass a body has the more force that is required to give it an acceleration. the mass of anobject appearing in the expression
Force = mass x acceleration is the inertial mass

(b)Any 3 correct factors
area exposed
humidity/dryness of the air
( c) Ice melts if ( sufficient) pressure is applied to it. This is because an increase in pressure lowers the melting point of ice. When the two ice cubes are pressed together, melting point of ice is lowered, so they melt to form a thin layer of water (between them). On releasing the pressure, the water formed freezes because decrease in pressure raises the freezing point. Hence the two cubes stick together.
(d)P =pgh
hAPA = hB PB
26xO.92x 103 =hBx 1.30 x 103
hB = 26xO.92x 103
1.30 x 103
= 18.4 cm

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