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igcse physics notesprinted 69 · PDF 69
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printed 69 · PDF 69
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69
Answers:
(a)(i) Pressure=Force/Area. The force exerted is equal to the weight which is
13000N. The area occupied by a tire is 0.016m2 and since there are four tires the
total area will be 4x0.016=0.064m2. Now pressure = 13000/0.064 so pressure=
203125 Pa or 200000 Pa to 2 sig figs.
(a)(ii) (This question is of four marks). Since the question is of four marks we
need to write four points to get full marks.
Firstly, when the car moves along the road instead of standing still, there will be a
force of friction on its tires that will oppose its motion.
This force will cause some of the car’s kinetic energy to be wasted by changing it
to heat energy, which will increase the temperature of the tires and heat them up.
A greater temperature of the tires will cause the air particles in the tire to have
greater energy so they will move faster.
The air particles will collide more frequently with the walls of the tire and exert a
greater force on them.
Since the force exerted on the tires is greater but the area of the tires is constant,
the tire pressure will increase.
(b) In this question, since temperature is constant, we can use Boyle’s law to
find out the new volume of helium gas when its pressure changes.
Boyle’s Law: P1V1=P2V2
2.0x106(0.026)=1.0x105(V2)
V2=52000/105 =0.52m3
New volume of helium gas is 0.52m3
Volume needed for one balloon to be filled=0.015m3
Max number of balloons filled= 0.52/0.015 =34.6667
Since only 34 full balloons can be filled, our answer is 34.
2)
Since this question is 3 marks we will need to give 3 valid points.
Pressure is force per unit area OR P=F/A
By lying down and spreading out his weight, the person is covering a much
greater area of the ground.