Class 8 Force and Pressure exercise question answer 8th general science
Class 8 general science chapter 3 question answer Class 8 question answer Force and pressure Force and pressure class 8 question answer maharshtra board
Q.1.Write proper word in the blank space.
a)The SI unit of force is ……………
(Dyne, Newton, Joule)
Ans: The SI unit of force is Newton
b. The air pressure on our body is equal to……….. pressure.
(Atmospheric, Sea bottom, Space)
Ans: The air pressure on our body is equal to Atmospheric pressure
c)For a given object, the buoyant force in liquids of different…. is…………… .
(the same, density, different, area)
Ans: For a given object, the buoyant force in liquids of different density is the same.
d. The SI unit of pressure is ……………
(N/m3 , N/m2 , kg/m2 , Pa/m2 )
Ans: The SI unit of pressure is N/m2.
Class 8 science chapter 3 question answer Maharashtra board Science digest std 8 maharashtra board Class 8 science chapter 3 8th general science question answer
Q.2. Make a match. A group B group
|
A group |
B group (Ans) |
|
1. Fluid |
e.Same pressure in all
directions |
|
2.Blunt knife |
d.Lower pressure |
|
3.Sharp needle |
a.Higher pressure |
|
4.Relative density |
c. Specific gravity |
|
5.Hecto Pascal |
b.Atmospheric Pressure |
Q.3. Answer the following questions in brief.
a. A plastic cube is released in water. Will it sink or come to the surface of water?
Ans:
1.A plastic cube will come to the surface of the water.
2.Because of the density of plastic cube is less than the water. When it floats, the unbalanced force acting on it is zero.
b. Why do the load carrying heavy vehicles have large number of wheels?
Ans:
1.The pressure produced by a given force depends on the area of the surface on which the force acts.
2.The greater the surface area, the less is the pressure produced.
3.Load carrying heavy vehicles have large number of wheels so that the load (weight, force) is disturbed over large surface area of the wheels in contact with the road.
Hence the pressure decreases and the tyre do not burst.
c. How much pressure do we carry on our heads? Why don’t we feel it?
Ans:
1.The air pressure at the sea called 1 atmosphere pressure.
2.The air pressure at the sea level is about 101*103 Pa. This is the pressure that we carry on our heads.
3.We don’t feel pressure because our body cavities filled with air, and arteries and veins are filled with blood. Their pressure balances the pressure due to the atmosphere.
Hence
we don’t feel atmospheric pressure.
Q.4. Why does it happen?
a. A ship dips to a larger depth in fresh water as compared to marine water.
Ans:
1.The buoyant force acting on a body is proportional to the density of the fluid in which the body is immersed.
2.The density of fresh water is less than that of marine water.
3.Hence, the buoyant force on a body in fresh water is less than that in marine water.
Therefore,
a ship dips to a larger depth in fresh
water as compared to marine water.
b. Fruits can easily be cut with a sharp knife.
Ans:
1.The effect of a given force varies inversely as the area of the surface on which the force is applied.
2.The less the surface areas, the greater is the effect of force.
3.The cutting edge of a sharp knife has less cross sectional area relative to that of blunt knife.
Hence,
it is easy to cut fruits with a sharp knife.
c. The wall of a dam is broad at its base. d. If a stationary bus suddenly speeds up, passengers are thrown in the backward direction.
Ans:
1.The pressure at a point in a liquid is proportional to the height of the liquid column above it.
Hence, the pressure of water in a dam is much greater at the bottom of the dam than at the top .
2.To
withstand this high pressure, the wall of a dam is made stronger and thicker
(broad) at the base than at the top.
d. If a stationary bus suddenly speeds up, passengers are thrown in the backward direction.
Ans:
When
passengers sit or stand in a stationary bus, they are in a state of rest. When
the us suddenly speed up, the lower parts of their body in contact with the bus
acquire the speed of the bus.
The
upper part of their body, however, continue to be in the state of rest due to
inertia.
Hence,
they are thrown in the backward direction.
8th science guide answer 8th standard general science question answer Class 8 general science question answer General science question answer for 8th class
Q.5. Complete the following tables.
|
Mass (kg) |
Volume (m3) |
Density (kg/m3) |
|
350 |
175 |
2 |
|
760 |
190 |
4 |
|
Density of Metal (kg/m3) |
Density of water (kg/m3) |
Relative Density) |
|
5 x
103 |
103 |
5 |
|
8.5 x
103 |
103 |
8.5 |
|
Weight (N) |
Area (m2) |
Pressure (Nm-2) |
|
800 |
0.04 |
20,000 |
|
1500 |
500 |
3 |
Q.6. The density of a metal is 10.8 x 103 kg/m3. Find the relative density of the metal.(Ans. 10.8)
Ans:
Data: Density of the metal = 10.8 x 103 kg/m3.
Density of water = 103 kg/m3
Relative density of a substance=
Density
of the substance / Density of the water
= 10.8 x 103 kg/m3 / 103 kg/m3
= 10.8 kg/m3.
Q.7. Volume of an object is 20 cm3 and the mass in 50 g. Density of water is 1 gcm-3. Will the object float on water or sink in water? (Ans: Sink)
Ans:
Given Data: m = 50g, V= 20 cm3, P(water)= 1 g/cm3
Density (P) = Mass/volume
= 50/20
= 2.5 g/cm3
It is greater than the density of water.
Hence
the body will sink in water.
General science question answer for 8th class 8th class science all question answer Class 8 general science chapter 3 question answer Class 8 question answer Force and pressure Force and pressure class 8 question answer maharshtra board
Q.8. The volume of a plastic covered sealed box is 350 cm3 and the box has a mass 500 g. Will the box float on water or sink in water? What will be the mass of water displaced by the box?
(Ans :
Sink, 350 g)
Ans:
Given Data: m= 500g, V = 350 cm3
P(water)= 1 g/cm3
Density (P) = Mass/volume
P (Body) = 500/350
= 10/7 g/cm
It is greater than that of water.
Hence, the box will sink in water.
The volume of water displaced by box (v) =
= the volume of the box = 350 cm3
Now, density (P) = mass/volume
= m = pV
The
mass of water displaced by the box = 1 g. cm3 x 350 cm3 = 350g.
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