Why
do water pipes burst in severe cold winters?
Ans:
Water freezes in pipes during winters, when the temperature goes below 0 degree
Celsius (i.e., freezing point of water). It expands and in the process exerts
pressure on the water pipes, thereby sometimes bursting them.
Most
aircrafts and ships have their front shape pointed. Why?
Ans: The
shape of many objects, viz. aeroplanes, rockets, ships, etc. moving through air
or water, are designed in such a way that friction can be reduced between the
objects and air/water. Such type of body is known as streamlined and the
process is known as streamlining.
An
athlete runs some distance before taking jump, why?
Ans: An
athlete runs a certain distance before actually jumping in order to increase
his speed, and thereby, his inertia of motion. This increased inertia of motion
enables him to jump a longer distance.
It is
difficult to drown in the Dead Sea. Why?
Ans: The
water of Dead Sea has a salt content of 27%. Therefore, its density is much
greater than that of ordinary sea water and it also offers a greater upthrust.
Hence, the body weighs less than an equal volume of Dead Sea water and is thus,
able to float.
Why
aquatic animals have soft skeleton unlike those of the terrestrial animals?
Ans: The
density of animals and fish living in water is almost the same as the density
of water. Therefore, their weight is almost completely balanced by buoyancy.
That is why they do not need massive skeleton like those of terrestrial
animals.
Why
does a swimming pool appear less deep than it really is?
Ans:
When rays of light start from the bottom of a pool and travel from water to
air, they are refracted away from the normal because they travel from a denser
medium to a rarer medium. As a result, a virtual image of bottom is formed
above the bottom. Hence, a swimming pool appears less deep than it really is.
Why
is electrical wiring in parallel better?
Ans:
electrical wiring in parallel is better because all the lines will have the
same potential difference and if one line gets fused the other lines remain
unaffected.
It is
easier to swim in sea water than in river water. Explain.
Ans: The
density of sea water is more than that of the river water. Therefore, the
weight of sea water displaced by the swimmer is more. Thus, buoyant force of
upthrust on the swimmer increases, making it easier to swim in sea water.
A
cold compress is applied on the forehead of a person suffering from high fever.
Why?
Ans:
Evaporation causes cooling. As the water evaporates, it absorbs heat from the
forehead and helps in reducing the temperature.
A man with a load his head
jumps from a high building. What will be the load experienced by him?
Ans:
Zero, because the acceleration of his fall is equal to the acceleration due to
gravity of the earth.
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