Dear students, prepare for physics class 9th chapter 7 long questions. These important long questions are carefully added to get you best preparation for your 9th class physics ch. 7 exams.

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##### Question: 1

Q no: 5 (A) Derive the formula of Young Modulus.?<div><br></div>

##### Answer: 1

1-24Young's Modulus:

The ratio of stress and strain is a constant within the elastic limit , this constant is called the young's Modulus.

Mathematical Form:

Consider a long bar of length Land cross- sectional area A let an external force F is equal to weight stretches it such that the stretched length becomes L.

_{o}Mathematically.

Young's Modulus = Y = Stress/Tensile strain

Let ▲L =L-L

_{o}Since-

Stress = Force/Area =F/A

And

Tensile strain = L-L

_{o}/L_{o}= ▲L/L_{o}As

Young's modulus = Y = Stress/Tensile strain

=F/A x L

_{o}/▲L = F x L

_{o}/A x▲L##### Question: 2

Q no 5 (B) How much would be the volume of ice formed by freezing 1 liter of water.

##### Answer: 2

2-24Data: = 109 liters Ans

Volume of water = V

_{1}= 1 liter Volume of ice on freezing=V_{2}= ?Solution:

As we know that Volume of ice/Volume of water =density of water/density of ice

Volume of ice = density of water/density of ice x Volume of water

= 1000/920 x 1

##### Question: 3

Q no<gwmw class="ginger-module-highlighter-mistake-type-6" id="gwmw-15861787112275774475990">:</gwmw>6 (A) State the Pascal's law. What are its applications in our daily <gwmw class="ginger-module-highlighter-mistake-type-6" id="gwmw-15861787268584093793150">life</gwmw>?

##### Answer: 3

3-24Pascal's Law:

Pressure applied at any point of liquid anclosed in a containeris transmitted without the loss to all other parts of the liquid.

An external force applied on the surface of a liquid increases the liquid pressure at the surface of the liquid. This increase in liquid pressure is transmitted equally to all direction and to the walls of the container in which it is filled.

Applications of Pascal's Law:

Hydraulic press is a machine which works on the principle which works on the principle of Pascal's law. It consists of two cylinders which are fitted with pistons of cross-sectional area a and A. The object is to be compressed is placed over the pistonof large cross- sectional areea A. The force is applied on the piston of cross-sectional area a .

The pressure P produced by small piston is transmitted through the liquid and acts on the large piston and a force Facts on

_{2}A Which is much larger than F .

_{1}

##### Question: 4

Q no 6B) Thedensity of air is 1.3 Find the mass of air in measuring 8m x 5m x 4m.

##### Answer: 4

4-24Data:m = ? m = 208kg Ans

= 1.3

v= 8m x 5m x 4m

= 160m

^{3}Solution:

As we know that

Density = Mass/Volume

Mass = Density x Volume

=1.3 x 160

##### Question: 5

Q no: 7 (A) Explain hydraulic press, on what principle does it work.

##### Answer: 5

5-24Data : p =?

F= 20N

L= 10mm

= 10 x 10m

^{-3}A= L x L = 10 x 10x 10 x 10

^{-3}^{-3} = 100 x 10

^{-6} = 1 x 10m

^{-4}^{2}

Solution:

As we know that

P = F/A

P= 20/1 x 10

^{-4}P= 20 x 10

^{4}P= 2 x 10Nm Ans

^{5}^{-2}##### Question: 6

Q no: 7B) State Archimedes principle and prove it and derive equation of up thrust of liquid.

##### Answer: 6

6-24Archimedes Principle:

When is totally or partially immersed in a liquid, an up thrust act on it equal to the weight of the liquid it displaces.

Explanation:

Consider a solid cylinder of cross-sectional area A and height h immersed in a liquid. Let h1 and h2 be the depth of the top and bottom surfaces of the liquid.

Then

h2-h1= h

If P1 and p2 are the pressures at the depth h1 and h2 p is its density, then

P1= pgh2

P2= fgh2

Let the force F1 is exerted the cylinder top by the liquid due to pressure P1 and the force F2 is exerted at the bottom of the cylinder due to P2

So

F1=pgh1A

F2=pgh2A

F1 and F2 are acting on the opposite faces of the cylinder. Therefore, the net force F will be F2- F1 in the direction of F2

F2 - F1 = pgh2A -pgh1A

=pgA ( h2-h1)

=pghA

= pgV

##### Question: 7

What are the features of kinetic molecular model of matter? explain the types of matter

##### Answer: 7

7-24Kinetic molecular model: the features of kinetic molecular model of matter is following

- Matter is made up of particles called molecules
- The molecules remain in continuous motion
- Molecules attract each other

##### Question: 8

What is density? explain

##### Answer: 8

8-24Density; density of a substance is defined as its mass per unit volume

Unit: its S.I unit is kilogram per cubic meter (kgm

^{-3})##### Question: 9

Define pressure. explain it with examples

##### Answer: 9

9-24Pressure; the force acting normally per unit area on the surface of a body is called pressure.

unit: its S.I unit is Nm-2 or pascal(Pa). Thus 1 Nm-2 =1Pa

Dependence; it depends upon area and applied force

##### Question: 10

Define atmospheric pressure . explain it

##### Answer: 10

10-24Atmospheric pressure ; the earth is surrounded by a covered of air called atmosphere. It extends to a few hundred kilometer above sea level. Air is mixture of gases. The density o air in the atmosphere is not uniform. It decrease s continuously as we go up. It acts in all directions

##### Question: 11

What is barometer? how atmospheric pressure is measured using a barometer

##### Answer: 11

11-24Barometer; the instrument that measure atmospheric pressure is called barometer.

##### Question: 12

Explain the variation in atmospheric pressure

##### Answer: 12

12-24Variation in atmospheric pressure : the atmospheric pressure decrease as we go up. The atmospheric pressure on mountain's is lower than at sea level. At a height above 30km, the atmospheric pressure becomes only7mm of mercury which is approximately 1000pa. It would becomes zero at an attitude where there is no air. Nearly half of its mass is between sea level and 10km. up to 30 km from sea level contains about 99% of the mass of the atmosphere. Thus, we can determine the altitude of a place by knowing the atmospheric pressure at that place.

Atmospheric pressure may also indicate a change in the weather . On a hot day, air above the earth becomes hot and expands. This causes a fall of atmospheric pressure in that region. On the other hand, during cold chilly nights, air above the earth cool down. This causes an increase in atmospheric pressure.

The changes in atmospheric pressure at a certain place indicate the expected changes in the weather condition of the place . For example, a gradual and average drop in atmospheric pressure means a low pressure in neighboring locality. Minor but rapid fall in atmospheric pressure indicates a windy and showery condition in nearby region. A decrease in atmospheric pressure is accompanied by breeze and rain. Whereas a sudden fall in atmospheric pressure often followed by a storm, rain and typhoon to occur in few hour time.

On the other hand, an increasing atmospheric pressure with a decline later on predicts an intense weather conditions. A gradual large increase in the atmospheric pressure indicates a long spell of pleasant weather .condition. A rapid increase in atmospheric pressure means that it will soon be followed by a decrease in atmospheric pressure indicating poor weather ahead.

##### Question: 13

Explain the application of atmospheric pressure in daily life

##### Answer: 13

13-24Application of atmospheric pressure: the applications of atmospheric pressure in daily life are following

- The fan in vacuum cleaner lower s air pressure in its bucket. The atmospheric air rushes into it carrying dust and dirt with tit through its intake port. The dust and dirt particles are blocked by the filter while air escapes out.
- When air is sucked through straw with its other end dipped in a liquid, the air pressure in the straw decrease. this causes the atmospheric pressure to push the liquid up the straw
- The air pressure inside the bubble and balloon is equal to atmospheric pressure
- The piston of the syringe is pulled out. This lowers the pressure in the cylinder . The liquid from the bottle enters into the piston through the needle.

##### Question: 14

Define pressure and also explain pressure in liquid

##### Answer: 14

14-24Pressure : the force exerted on unit area is known as pressure.

##### Question: 15

State and explain Pascals law

##### Answer: 15

15-24Pascals law: pressure applied at any point of a liquid enclosed in a container, is transmitted without loss to all other parts of liquid

##### Question: 16

Explain breaking system in vehicles

##### Answer: 16

16-24Breaking system in vehicles: the braking system of cars, buses , etc. also work on Pascals law. The hydraulic breaks allow equal pressure to be transmitted throughout the liquid. When break pedal is pushed, it exerts a force on the master cylinder, which increases the liquid pressure in it. The liquid pressure is transmitted equally through the liquid in the metal pipes to all the pistons of other cylinder s. Due to the increase in liquid pressure, the piston in the cylinders move outward pressings the break pads with the brake drums. The force of friction between the brake pads and the brake drums stops the wheels.

##### Question: 17

Explain working of hydraulic press on the basis of Pascal's law.

##### Answer: 17

17-24Hydraulic press: hydraulic press works on Pascal's law

##### Question: 18

State and explain Archimedes principle. Also prove it

##### Answer: 18

18-24Archimedes principle: when a body is totally or partially immersed in a liquid, an upthrust acts on it equal to the weight of the liquid it displaces

##### Question: 19

How we can find the density of an object<div><br></div>

##### Answer: 19

19-24Density of an object: Archimededs principle is also helpful to determine the density of an object. The ration in the weight of a body wiht an equal volume of liquid is the same as in theri densitites.

Density of object = D

Density of liquid= p

Weight of object = w1

Weight of equal volume of liquid = w= w1-w2

here w2 is the weight of the solid in liquid. According to archimedes principle, w2 is less than its actual weight w1 by an amount w.

##### Question: 20

What is the principle of floatation. explain

##### Answer: 20

20-24Principle of floatation: a floating object displaces a fluid having weight equal to the weight of the object.

Example: an object sinks if its weight is greater than the upthrust acting on it. An object floats if its weight is equal or less than upthrust . When an object floats in a fluid, the upthrust acting on it is equal to the weight of object. In case of floating object, the object equal to the weight of the fluid displaced by the object. This is the principle of floatation. It is applicable on liquid as well as gases.

##### Question: 21

Explain how submarine moves up the water surface down into water

##### Answer: 21

21-24Submarines: a submarine can travel over as well as under water. it also work on the principle of floatation. I t floats over water when the weight of water is equal to its volume is greater than its weight. Under this condition , it is similar to a ship and remains partially above water level. It has a system of tanks which can be filed with and emptied from seawater. When these tanks are filed with seawater, the weight of the submarine increases. As son as its weight becomes greater than the upthrust, it dives into water and remains under water . To com up on the surface, the tanks are emptied from sea water.

##### Question: 22

Define elasticity. explain deforming force, stress, strain and tensile strain.

##### Answer: 22

22-24Elasticity: the property of a body to restore its original shape and size as the deformation force ceases to act is called elasticity.

##### Question: 23

State and explain Hook's law

##### Answer: 23

23-24Hook's law: the strain produced in a body by the stress applied to it is directly proportional to the stress with in the elastic limit of the body

##### Question: 24

State and explain Young's modulus.

##### Answer: 24

24-24Young' modulus; the ratio of stress to tensile strain is called young's modulus.