Question

Give reason for following:
1) it is easier to cut with a sharp knife than with a blunt one.
2) Sleepers are laid below the rails.
3) A gas bubble grows in size as it rises to the surface of a lake.
4) Ship made of iron floats in water but an iron nail sinks.
5) it is easier for a man to swim in seawater than in freshwater.

Answer 1

1) because the area on which force is applied is lesser in a sharp knife , so pressure applied is More and it's easier to cut

Answer 2

1) The pressure exerted by the sharp knife edge is more than that exerted by the blunt one because the area on which force is exerted with a sharp knife is very small. Thus, it is easier to cut with the former than with the latter.
2) The pressure on a surface is reduced b distributing thrust on a larger surface area. Wide sleepers are laid down below the rail tracks so that the pressure exerted by the rails on ground becomes less.
3) At any point under the surface of liquid, pressure is proportional to its depth. As the bubble rises up, pressure of liquid surrounding it reduces which is balance by increasing its volume. (Boyl's law: PV = const).
4) As the density of an iron nail is more than that of water, the nail sinks in water. ... The volume of water displaced is much greater than the volume of the iron ship. Hence, according to Archimedes' principle, the upthrust is more than the weight of the ship. That is why the iron ship floats in water.
5) When salt is dissolved in water, as it is in ocean water, that dissolved salt adds to the mass of the water and makes the water denser than it would be without salt. Because objects float better on a dense surface, they float better on salt water than fresh water.



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