Chapter : 2 Pressure All Give reason question answer:
Give reason question and ans:
1. Why do sea drivers wear well designed suits?
As the depth of the sea increases, the
pressure increases since pressure increases with depth. The pressure exerted by
water deep under the sea is much greater than at the sea level. Hence, the deep
sea divers wear special suits which protect them from extreme pressure of
water. These suits are called diving suits. These suits contain buoyancy
compensators to combat the weight of their diving equipment and the pressure of
water at great depths.
2. A bucket is filled faster at the lower stairs
than at the upper stairs. why?
We can fill a bucket from
downstairs tap quicker than from an upstairs tap because due to gravitational
Force the water exerts more pressure in downstairs tap as compared to upstairs
tap. The water will come out of tap with a great force of pressure.
Or,
We know that the liquid
pressure is directly proportional to the depth or height, For top stair depth
is low and for upstairs depth or height is high so more pressure is applied to
it and more force is applied therefore A bucket is filled faster at the lower
stairs than at the upper stairs.
3. The blood pressure
in humans is greater at the feet than at the brain
The pressure of a liquid is given by the relation:
P = hdg
Where,
P = Pressure
h = Height of the liquid column
d = Density of the liquid
g = Acceleration due to the gravity
It can be inferred that pressure is directly proportional to
height. Hence, the blood pressure in human vessels depends on the height of the
blood column in the body. The height of the blood column is more at the feet
than it is at the brain. Hence, the blood pressure at the feet is more than it
is at the brain.
4. An egg floats on salty water but sink in pure water. why?
Because the density of
the egg is higher than the density of tap water,
so it sinks, When enough salt is added to the water,
the saltwater solution's density becomes higher, if density is increased then
Upthrust is high, so the egg will be float.
5. An iron nail sinks in
water but a ship made of iron floats.
It’s because an iron ship is not completely
solid. It has full of air filled in it. So the average density of the ship as a
whole is less than the density of water. Therefore immersed portion of the ship
displaces water equal to its weight. So the ship floats whereas a sheet of iron
is compact and there are no air spaces inside it. Iron is denser than that of
water. The weight of the sheet is greater than the weight of the water
displaced by the sheet. So it sinks.
6. Why water pump cannot lift water more than 10 meters high
from the earth surface?
Because a water
pump is based on the principle of atmospheric pressure. Atmospheric
pressure cannot push up water up to 10 metre high. At
above 10 m atmospheric pressure is become low. So, water pump cannot lift water more than 10 meters
high
7. Why can water not be used in barometric liquid?
water cannot be used as
barometric liquid because it's density is lower than Mercury .water's density
is 1000 gram per cubic meter.hence it requires a barometer whose height is
around 11 meters.
8. The bottom of dam is wider and stronger than upper part.OR Walls of a dam are made thicker at the bottom. Why?
Liquid pressure is
directly proportional to the depth of liquid from free surface. At the bottom
of dam, there is high water pressure. To protect the dam from the high water
pressure, the bottom is made wide and stronger than the upper part.
9. The pressure exerted by water at the bottom of the drum decreases slightly at the Himalayan region than that in the Terai region.
Since pressure of a liquid
is directly proportional to the value of g and the value of g is more at
Terai region than that in the Himalayan region. So, the pressure exerted by
water at the bottom of the drum decreases slightly at the Himalayan region
than that in the Terai region.
10. The bucket filled faster in the downstairs tap than in upstairs tap.
Pressure of a liquid is
directly proportional to its depth or height from the free surface.
The tap at the downstairs is at greater height than the tap at the upstairs.
Water comes out with greater pressure from the downstairs tap. So, bucket is
filled faster in the downstairs tap than in upstairs tap.
11. The speed of flow of water out of a tap of upper floor is less than that of the down floor.
Since pressure of a liquid
is directly proportional to its depth or height from the free surface. The
height of the liquid column on the down floor is more than that on the upper
floor. So the speed flow of water out of a tap of upper floor is less than that
of the down floor.
12. A deep sea-diver needs to wear diving suit.
The pressure of a liquid
is directly proportional to the height of liquid column from free surface.
When a person dives deep into sea, he or she has to bear high water pressure.
To withstand with high water pressure, it is necessary to wear diving suit.
13. Weight of stone decreases in the salt solution.
When salt is dissolved
in water, the upthrust increases due to the increases in the density of water .
As a result, the weight of a stone decreases in the salt solution.
14. It is easier to lift a heavy stone inside the water.
The weight of the stone
inside the water decreases due to the upthrust. So it is easier to lift a
heavy stone inside the water.
15. The weight of a body is lighter in water than in air.
Upthrust due to water is
greater than that of air. Upthrust decreases weight of body. Hence, the weight
of a body is lighter in water than in air.
16. The weight of a body is more in vacuum than in air.
There is no upthrust in
vacuum. Upthrust decreases the weight of body. Hence, the weight of body is
less in air due to its upthrust.
17. It is easier to pull a bucket of water from the well until it is inside the water but difficult when it is out of water.
Upthrust due to
water is greater than that of air. Upthrust exerted by water decreases weight
of body. Hence, it is easier to pull a bucket of water from the well until it
is inside the water but difficult when it is out of water.
18. Studs are made on the sole of football player’s boot.
P = F/A
Studs are made on the
sole of football player’s boot to increase the pressure on the ground that
prevents the player from falling or sliding during sudden run and turning.
19. It is easier to cut vegetables with the sharp-edged knife than the blunt one.
The area of the edge of
sharp knife is less than that of the blunt one. So sharp-edged knife can exert
more pressure while applying force than that of the blunt edged knife as the
pressure is inversely proportional to the area. Due to more pressure, it is
easier to cut vegetables with the sharp-edged knife than the blunt one.
20. Buses and trucks have broad and double wheeled tyres.
The buses and trucks have
to carry greater weight which exerts greater pressure on the tyres. The pressure
on them is reduces by increasing the area of the tyres as the pressure is
inversely proportional to the area.
21. Camel can walk easily on sand.
Camel has flat-soled feet
which exert less pressure due to the body weight of camel. As there is less
pressure exerted by flat-soled feet of camel, it can easily walk on
the sand.
22. The wheel of tractor is wider than that of a car.
The rear wheels of a tractor
are made large and flat to reduce the pressure and prevent the tyres from
descending into the muddy land. As tractor is used for ploughing and threshing
in crop fields, small and narrow real wheels may descent into the muddy and
marshy load due to more pressure.
23. The water supply tanks are placed higher than any other building in a town.
The water supply tanks
are placed higher than any other building in a town so that the pressure of
water is more. Due to this, water can flow to the buildings located at higher
level. As a result, water can be supplied easily on the taps of uppermost
floors and houses built at higher level of ground.
24. The gravity bulb of hydrometer is made heavier.
The gravity bulb of
hydrometer is made heavier so that its centre of gravity remains very low,
when it is floating in denser liquids. It helps the hydrometer to float
upright in stable equilibrium.
25. Hydrometer has a heavy bulb and narrow stem.
Hydrometer has a heavy
bulb to float in a liquid vertically. The stem of hydrometer is made long
and narrow to find the relative density of less dense liquid i.e. it
increase its sensitivity.
26. The floatation bulb (buoyancy bulb) of hydrometer is made small.
The floatation bulb of
hydrometer is made small because denser liquids provide more upthrust and
hence the whole hydrometer does not float on the dense liquid.
27. An egg sinks in fresh water but floats in a strong solution of salt (or in a saturated salt solution).
Fresh water has less density
than that of the egg so the egg cannot displace water equal to its weight and
it sinks. But salt on mixing with water increases the density of water which
increase upthrust and hence the egg can displace water equal to its weight and
floats.
28. Iceberg made up of water floats in water.
The density of ice is
less than that of water. Due to this, iceberg is able to displace the water
equal to its weight. Hence, Iceberg made up of water floats in water.
29. An iron nail sinks in water but a ship made up of iron floats.
Since the density of
iron is greater than that of water, the iron nail sinks as the weight of the
nail is greater than the weight of the displaced water. But the ship made of
up iron is designed in such a way that the relative density of ship becomes
always less than that of water. Hence, the weight of water displaced becomes
equal to the total weight of the ship and the ship floats.
30. It is easier for a man to swim in sea water than in river water.
The density of sea water
is more than that of river water. Thus for the same volume, the sea
water provides more upthrust as compared to the river water. So it is easier
for a man to swim in sea water than in river water.
31. A hole at the bottom of a boat is more dangerous than that at the side.
The bottom of the boat
exerts more pressure, as the force acts perpendicularly downwards, than
that at the sides. If there is hole at the bottom of the boat, more water
enters inside due to more upthrust and the boat may sink. So, a hole at the bottom
of a boat is more dangerous than that at the side.
32. An iron nail sinks in water but floats in mercury.
The density of iron is
more than that of the water. The iron nail cannot displace the eater equal to
its weight and it sink. But the density of mercury is much more than that of
the water. It gives more upthrust which helps the iron nail to float on
mercury.
33. A girl with heeled shoe exerts a higher pressure on the ground than an elephant.
The area of the heels of
the girl’s shoes is much smaller in comparison with the area covered by the
flat feet of the elephant. As a girl with heeled shoe exerts
a higher pressure on the ground than an elephant.
34. A man exerts more pressure under his foot when he stands with one foot than when he stands on two feet.
The area of one foot is
less than that of two feet. As so a man exerts more pressure
under his foot when he stands with one foot than when he stands on
two feet.
35. The base of the house is made wider than its wall.
The walls and roof of
house exerts pressure on the base of a house. The pressure exerted by the
building is reduced by making the base of the house wider as pressure is
inversely proportional to the area.
36. The loaded ship sinks more than empty ship.
The loaded ship has
larger mass. Hence, the weight (or volume) of displaced water is more for
loaded ship. But the empty ship has lesser mass. Hence, the weight (or volume)
of displaced water is less for empty ship. So the loaded ship sinks more than
empty ship.
END............
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