Physics
It takes much longer to cook food in the hills than in the plains, because

in the hills the atmospheric density is low and therefore a lot of heat is lost to the atmosphere
due to low atmospheric pressure on the hills, the water boils at a temperature higher than 100oC and therefore water takes longer to boil
in the hills the humidity is high and therefore a lot of heat is absorbed by the atmosphere leaving very little heat for cooking
n the hills the atmospheric pressure is lower than that in the plains and therefore water boils at a temperature lower than 100oC causing an increase in cooking time

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Physics
Light houses are places with powerful lights to :

Indicate to the incoming warships, the location of a harbour during night
Guide and resolve traffic jams in crowded metro-cities during nights
Guide and help large crowds at religious gathering during nights
Guide and warn the ships coming from different directions in the ocean

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