# Pressure in Fluids Exe-4A Short Answer Physics Class-9 ICSE Selina Publishers

Pressure in Fluids and Atmospheric Pressure Exe-4A Pressure in Fluids and it’s Transmission Short Answer Type for Class-9 ICSE Concise Physics. There is the solutions of short Answer type Questions of your latest textbook which is applicable in 2023-24 academic sessionVisit official Website CISCE for detail information about ICSE Board Class-9.

## Pressure in Fluids and it’s Transmission Exe-4A Short Answer

(ICSE Class – 9 Physics Concise Selina Publishers)

 Board ICSE Class 9th Subject Physics Writer / Publication Concise selina Publishers Chapter-4 Pressure in Fluids and Atmospheric Pressure Exe – 4A Pressure in Fluids and it’s Transmission Topics Solution of Exe-4(A) Short Answer Type Academic Session 2023-2024

#### Exe-4A Pressure in Fluids and it’s Transmission Short Answer Type

Ch-4 Pressure in Fluids and Atmospheric Pressure Physics Class-9 ICSE Concise

Page 102

#### Question 1. What is meant by pressure? State its S.I. unit.

Pressure is the thrust per unit area of the surface.

Its S.I. unit is ‘newton per meter2‘ or ‘pascal’.

#### Question 2. Differentiate between thrust and pressure.

Thrust is the force applied on a surface in a perpendicular direction and it is a vector quantity. The effect of thrust per unit area is pressure, and it is a scalar quantity.

#### Pressure in Fluids and Atmospheric Pressure Exe-4A Short Class-9 ICSE

Ch-4 Pressure in Fluids and Atmospheric Pressure Physics Class-9 ICSE Concise

Page 103

#### Question 3. How does the pressure exerted by thrust depend on the area of surface on which it acts? Explain with a suitable example.

Pressure exerted by thrust is inversely proportional to area of surface on which it acts. Thus, larger the area on which the thrust acts, lesser is the pressure exerted by it.

Example: If we stand on loose sand, our feet sink into the sand, but if we lie on that sand, our body does not sink into the sand. In both the cases, the thrust exerted on the sand is equal (equal to the weight of the body). However, when we lie on sand, the thrust acts on a large area and when we stand, the same thrust acts on a small area.

#### Question 4. Why is the tip of an allpin made sharp?

The tip of an allpin is made sharp so that large pressure is exerted at the sharp end and it can be driven into with less effort.

#### Question 5. Explain the following :

(a) It is easier to cut with a sharp knife than with a blunt one.

(b) Sleepers are laid below the rails.

(a) It is easier to cut with a sharp knife because even a small thrust causes great pressure at the edges and cutting can be done with less effort.

(b) Wide wooden sleepers are placed below the railway tracks so that the pressure exerted by the rails on the ground becomes less.

#### Question 6. What do you mean by the term fluid pressure?

Due to its weight, a fluid exerts pressure in all directions; the pressure exerted by the fluid is called fluid pressure.

#### Question 7. How does the pressure exerted by a solid and fluid differ?

A solid exerts pressure only on the surface on which it is placed, i.e. at its bottom, but a fluid exerts pressure at all points in all directions.

#### Question 8. State three factors on which the pressure at a point in a liquid depends.

Pressure at a point in a liquid depends upon the following three factors:

(i) Depth of the point below the free surface.

(ii) Density of liquid.

(iii) Acceleration due to gravity.

#### Question 9. Write an expression for the pressure at a point inside a liquid. Explain the meaning of the symbols used.

P = Po + h g

Here, P = Pressure exerted at a point in the liquid

Po = Atmospheric pressure

h = Depth of the point below the free surface

= Density of the liquid

g = Acceleration due to gravity

#### Question 10. How does the pressure at a certain depth in sea water differ from that at the same depth in river water? Explain your answer.

Due to dissolved salts, density of sea water is more than the density of river water, so pressure at a certain depth in sea water is more than that at the same depth in river water.

#### Question 11. Explain why a gas bubble released at the bottom of a lake grows in size as it rises to the surface of the lake.

The reason is that when the bubble is at the bottom of the lake, total pressure exerted on it is the atmospheric pressure plus the pressure due to water column. As the gas bubble rises, due to decrease in depth the pressure due to water column decreases. By Boyle’s law, PV = constant, so the volume of bubble increases due to decrease in pressure, i.e., the bubble grows in size.

#### Question 12. A dam has broader walls at the bottom than at the top. Explain.

The pressure exerted by a liquid increases with its depth. Thus as depth increases, more and more pressure is exerted by water on wall of the dam. A thicker wall is required to withstand greater pressure, therefore, the thickness of the wall of dam increases towards the bottom.

#### Question 13. Why do sea divers need special protective suit?

The sea divers need special protective suit to wear because in deep sea, the total pressure exerted on the diver’s body is much more than his blood pressure. To withstand it, he needs to wear a special protective suit.

#### Question 14. State the laws of liquid pressure.

Laws of liquid pressure:

(i) Pressure at a point inside the liquid increases with the depth from its free surface.

(ii) In a stationary liquid, pressure is same at all points on a horizontal plane.

(iii) Pressure is same in all directions about a point in the liquid.

(iv) Pressure at same depth is different in different liquids. It increases with the increase in the density of liquid.

(v) A liquid seeks its own level.

#### Question 15. A tall vertical cylinder filled with water is kept on a horizontal table top. Two small holes A and B are made on the wall of the cylinder, one near the bottom and other just below the free surface of water. State and explain your observation.

The liquid from hole B reaches a greater distance on the horizontal surface than that from hole A.

This explains that liquid pressure at a point increases with the depth of point from the free surface.

#### Question 16. Name and state the principle on which a hydraulic press works. Write one use of hydraulic press.

Hydraulic press works on principle of hydraulic machine.

It states that a small force applied on a smaller piston is transmitted to produce a large force on the bigger piston.

Use: It is used for squeezing oil out of linseed and cotton seeds.

—  : End of Pressure in Fluids and it’s Transmission Exe-4A Short Answer Type  Solutions :–

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