To further elaborate:

Quote:
More stirring is needed when sugar is dissolved in cold coffee than in hot coffee ?

In hot coffee, the kinetic energy of the molecules is greater because of the high temperature range in it. According to kinetic molecular theory this is not possible in cold coffee. So it is difficult to dissolve sugar in it.

The saturation capacity of any liquid is low during low level of kinetic energy of its molecules. When we increase the kinetic energy by heating or stirring the solute content holding capacity of liquid molecules is increased likewise its saturation level also increased and it can hold more sugar contents.

Quote:
A ball dropped vertically on the ground does not rise to its original height ?

The ball pushes itself back as per Newton's third law of motion every action has reaction in same amount but in opposite direction. When ball hit on the ground, its kinetic energy is converted into heat and sound. During bounce, it has to pass through the surrounding air and move with the force of gravity. During its way to ground gravitation force help it while during its way back gravitation force hinder its movement. the friction from surrounding air and also consumes its kinetic energy so with the efforts of heat, sound, gravitational force and friction of surrounding air the ball cannot reach upto the level of its drop.

5. How does the pouring of kerosene oil on stagnant on stagnant water contribute to the eradication of malaria ?

malaria is caused by a micro organism 'plasmodium' which lives in Anophelas mosquitoes (perhaps there are two main types of mosquitos perhaps first is cules and anophelas- culex infect birds while anophelas to animals).

mosquito goes through different stages during its development/growth i.e. egg, larvae, pupae and flying mosquito. first three stages are completed in water.

mosquito lay eggs on stagnant water. when keronsene oil is poured in small ponds of stagnant water it covers its upper layer and do not allow air to move inside layers of the water pond. the larvae of mosquito needs air/oxygen to breath, and it come from time to time on water layer to breath, in absence of oxygen mosquito larvae die out. the same process is related with other water animals like fish, if oil is poured into water then animal life inside that water is disturbed badly. other forms of oil can also be utilized but kerosene oil is a bit cheap thats why it is favoured.

i rememberd four five years back that in front plot of my home there was stangnant water, we got petrol from the vehicle and poured on the water and after some time we lit it and with a flash of fire all petrol burnt down and many mosquito larvae-which came near layer of water died out and we witnessed their dead bodies flowing in water...

6. Why is it dangerous to have charcoal fire burning in a badly ventilated room ?

charcoal require oxygen to burn and to produce carbon dioxide, if it is burnt in badly vetilated room tu it can utilize al of its oxygen and producing much carbon dioxide and life can be fatal in such room. further the fume badly detriot the lungs and respiratory passage....

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