K.C.S.E Physics Q & A - MODEL 2016PP1QN14

K.C.S.E Physics Q & A - MODEL 2016PP1QN14

a) Explain why it is advisable to use a pressure cooker for cooking at high altitudes 

b) Water of mass 3.0kg initially at 20⁰C is heated in an electric kettle rated 3.0KW. The water is heated until it boils at 100⁰C. (Take specific heat capacity of water 4200Jkg1K^-1. Heat capacity of the kettle = 450JK^-1, Specific latent heat of vaporization of water = 2.3Mjkg^-1)

Determine
(i) The heat absorbed by the water. 
ii)Heat absorbed by the electric kettle 
iii) The time taken for the water to boil 
iv) How much longer it will take to boil away all the water.

ANSWERS

​(a) At high altitudes pressure is low so boiling point is low
A pressure cooker increases pressure inside it which raises the boiling point hence faster cooking