Maharashtra Board Class 8 Science Solution Chapter 3 – Force and Pressure
Balbharati Maharashtra Board Class 8 Science Solution Chapter 3: Force and Pressure. Marathi or English Medium Students of Class 8 get here Force and Pressure full Exercise Solution.
Std |
Maharashtra Class 8 |
Subject |
General Science Solution |
Chapter |
Force and Pressure |
Exercise Solution
(1.) Write proper word in the blank space.
a.) The SI unit of force is ……………
(Dyne, Newton, Joule)
Answer: Newton.
b.) The air pressure on our body is equal to……….. pressure.
(Atmospheric, Sea bottom, Space)
Ans. Atmospheric
c.) For a given object, the buoyant force in liquids of different…. is…………… .
(the same, density, different, area)
Ans. Density, Different.
d.) The SI unit of pressure is ……………
(N/m^{3} , N/m^{2} , kg/m^{2}, Pa/m^{2} )
Ans. N/m^{2}
(2.) Make a match
Group A | Group B |
1. Fluid | a. Higher pressure |
2. Blunt knife | b. Atmospheric Pressure |
3. Sharp needle | c. Specific gravity |
4. Relative density | d. Lower pressure |
5. Hecto Pascal | e. Same pressure in all directions |
Answer:
Group A | Group B |
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 |
(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?
Answer: A plastic cube is released in water. It will float on water. Try & push it into the water. even when it pushed, it continues to float.
The empty plastic cube floats on the surface of water. Because the weight of empty cube is negligible as compared with the weight of weight inside. Thatswhy the plastic cube does not submerged on the water & it float on water.
b.) Why do the load carrying heavy vehicles have large number of wheels?
Ans. The large number of wheels of vehicles becomes easy to distribute the entire pressure of loads. As the load carrying large & heavy vehicle more & wide area of the vehicles. It will apply more pressure in ratio to its area & weight. To distribute this pressure, there will be need to force.
Because, more pressure need more force. Thus many number of wheels of a vehicles would be used.
c.) How much pressure do we carry on our heads? Why don’t we feel it?
Ans. We know, Atmospheric Pressure = 101325 pa
Area of your head (approx) = 50 x 50 centimeter square.
The pressure exerted by the air is 14 pounds per sq. inch at sea level. It is acting not only on the head, but on the whole body from all sides. We don’t feel it because, our body exits more or less equal pressure outwards. There by it gets balanced.
(4.) Why does it happen?
a.) A ship dips to a larger depth in fresh water as compared to marine water
Ans. A ship dips to a larger depth in fresh water as compared to marine water due to higher water density. The marine water is more dense than the fresh water. Marin water is more salty then fresh water. So marine water provides more buoyancy then fresh water. A ship shall sink inside water untill it displaces the amount of water that equates its own weight.
b.) Fruits can easily be cut with a sharp knife.
Ans. Fruits can easily be cut with a sharp knife. For organic matter, such as fruit, cutting is straight forward process. As a result the molecules of organic matter is much more flexible & the molecules find through weak intermolecular interaction.
c.) The wall of a dam is broad at its base.
Ans. The wall of a dam is broad at its base. Because the dam contains huge amount of water and as we go deep the pressure exerted by such a huge amount of water increases to very high. So pressure of water increases as the depth increases. Thats way Dams are designed broad at the bottom & narrow at the top.
d.) If a stationary bus suddenly speeds up, passengers are thrown in the backward direction.
Ans. Due to inertia of the state of rest the passengers are thrown in the backward direction. When the bus stay in its rest condition, then passengers are also state of rest due to Inertia, But suddenly bus speeds up & it moves to inertia of motion condition. But passengers still maintain their inertia of rest condition & they are thrown in the backward.
(5.) Complete the following tables.
Mass (kg) | Volume (m^{3}) | Density (kg/m^{3}) |
350 | 175 | |
190 | 4 |
Density of Metal (kg/m^{3}) | Density of water (kg/m^{3}) | Relative Density |
10^{3} | 5 | |
8.5 x 10^{3} | 10^{3} |
Weight (N) | Area (m^{2}) | Pressure (Nm^{2}) |
0.04 | 20,000 | |
1500 | 500 |
Solution:
(6.) The density of a metal is 10.8 x 10^{3} kg/m^{3}. Find the relative density of the metal.
Solution: We know that, Relative density = Density of metal / Density of Water = 10.8 x 10^{3} / 10^{3}
= 10.8 (Ans)
(7.) Volume of an object is 20 cm^{3} and the mass in 50 g. Density of water is 1 gcm^{-3}. Will the object float on water or sink in water?
Solution: Given data –
Volume = 20 cm^{3}, mass = 50 g, Density of water =1 gcm^{-3}
Therefore, Density = Mass/Vol = 50/20 = 5/2 g/cm^{3}
According to Archimedes principle, when the piece is dipped in water. Water of volume equal to the volume of the object i.e, 20 cc will be displaced. The loss in the weight of the object will be equal to the weight of displaced water 20 g.
Therefore, Weight of water = 50 – 20 = 30 g.
Therefore, It is sink in water.
(8.) The volume of a plastic covered sealed box is 350 cm^{3} 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?
Solution: Volume of box = 350 cm^{3}
Mass of box = 500 g.
Therefore, According to Archimedes principle water of volume equal to the volume of the box i.e. 350 cc will be displaced. The loss in the weight of box will be equal to the weight of displaced water 350 g.
Therefore, It is sink in water.
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