Many candidates did well in this question. Part (a)(i) was on the principle of conservation of energy and it was rendered with difficulty by just a few candidates. It proved a very familiar item to the generality of candidates. In part (a)(ii), the performance of the candidates was fairly satisfactory. Most of the candidates were able to draw the correct diagram but failed to explain it.
In part(b)(i) on the description of the experiment to determine the specific heat capacity of a solid by the method of mixtures recorded a lot of weaknesses. These include:
- inability to draw a complete and correctly labeled diagram for the experimental set up.
- Inability to present a clear sequential description of the experiments.
Part (b) (ii) was the precaution taken to ensure accurate results. The performance of the candidates was fairly satisfactory.
The expected answers are:
(i) In a closed system, the total energy is always a constant
OR
Energy can neither be created nor destroyed but can be transformed from one form to another.
(ii)
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As the pendulum bob moves towards the maximum displacement position, its speed decreases as the height above the reference point increases.
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Kinetic energy decreases while the potential energy increases
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The potential energy becomes maximum at the point of maximum displacement while the kinetic energy becomes zero.
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As the pendulum bob moves towards the equilibrium position, its potential energy reduces while the kinetic energy increases until the kE is maximum at the equilibrium position while PE becomes zero.
(b)(i) Procedure
- Weight the solid and record its mass ms
- Weigh the calorimeter and record the mass mc
- Fill the calorimeter with water (about 2/3 full) weigh the calorimeter and water and record the mass М
- Heat the solid in boiling water for some time and measure and record its temperature θs
- Measure and record the temperature θi of the water in the calorimeter
- Quickly transfer the hot solid into the water in the calorimeter
- Stir the mixture gently for some time, read and record the steady
temperature θf of the mixture.
Calculations
Heat lost by hot solid = Heat gained by water + [calorimeter and stirrer]
Ms Cs (θs - θf) = McCc (θ f + θi ) + (M - mc) cw (θ f - θi)
Cs = {McCc + (M – mc)cw} [θ f - θi]
Ms (θs - θf)
(ii) Any two valid precautions
e.g.
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Avoid spillage
-
Transfer solid quickly
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Avoid parallax in reading thermometer.
