K.C.S.E Physics Q & A - MODEL 2014PP1QN17

K.C.S.E Physics Q & A - MODEL 2014PP1QN17

(a) A long horizontal capillary tube of uniform bore sealed at one end contains dry air trapped by a drop of mercury. The length of the air column is 142 mm at 17°C.
Determine the length of the air column at 25°C.
(b) The pressure of the air inside a car tyre increases if the car stands out in the sun for some time on a hot day. Explain the pressure increase in terms of the kinetic theory of gases.
(c) In an experiment to determine the specific latent heat of vaporization of water, steam of mass 10g at 100°C is passed into 100 g of water initially at 20°C in a container of negligible heat capacity. The temperature of the water rises to 70°C.
(Take the specific heat capacity of water as 4.2 X 10³ J kg^-1 K^-1(and the boiling point of water as 100°C)
(i) Determine the specific latent heat of vaporization of water.
(ii) State two sources of error in this experiment.

answers

​(b) In the hot sun the temperature of the air increases; therefore the speed of the air molecules increases hence the rate of collisions between the molecules and tyre increases; The rate of change of momentum (pressure) of the molecules also increases.