Pressure

1 mark questions
1. Define the term pressure. What is its unit?
Ans: Force acting per unit area is called pressure. its unit is N/m2 or pascal(pa).
2. Define one Pascal pressure.
Ans: When a force of 1N is applied on 1m² area it is called 1 pascal pressure.
3. Define liquid pressure.
Ans: The pressure exerted by a liquid in certain area is called liquid pressure.
4. Write the factors on which liquid pressure depend.
Ans: The factors on which liquid pressure depend on are density of liquid (d), depth of liquid(h) and acceleration due to gravity(g).
5. What do you mean by atmospheric pressure?
Ans: The exerted by column of air above us is called atmospheric pressure.
6. What so you man by the statement that “atmospheric pressure of a place is 760 mm Hg?
Ans: The atmospheric pressure at sea level, the level of mercury inside the mercury barometer rises up to 760 mm.
7. What is liquid pressure? Write its SI unit.
Ans: The pressure exerted by a liquid in certain area is called liquid pressure. Its SI unit is Pascal (Pa).
8. What is standard atmospheric pressure?
Ans: The standard atmospheric pressure at sea level is 760 mm of Hg or 101300 N/m2.
9. Why is barometer used? Write.
Ans: Barometer is used to measure the atmospheric pressure.
10. State Archimedes' principle.
Ans: Archimedes' principle states that "When a body is wholly or partially immersed in liquid it experiences a loss in weight due to the upthrust which is equal to the weight of liquid displaced by it."
11. Write the application of Archimedes’ principle?
Ans: The application of Archimedes' principle are: boat and Ship.     
12. State Law of flotation.
Ans: Law of flotation states that 'A floating body displaces the liquid equal to its own weight.'
13. Write the application of Law of flotation.
Ans: The application of law of flotation are: Hydrometer and latecomer.
14. What is upthrust or buyouncy? Give its SI unit.
Ans: The resultant force experienced by an object when it is partially or wholly immersed inside a liquid is called upthrust or buyouncy. Its SI unit is N.
15. What are the factors on which Upthrust depend?
Ans: The factors on which up-thrust depend are: a. volume of an object   b. acceleration due to gravity  c. density of liquid.
16. On what condition does a body heavier than water float upon water?
Ans: A body heavier than water will float on it if it can displace the water equal to the weight of the body.
17. What is density?
Ans: Density is defined as the mass per unit volume.
18. What is relative density?
Ans: Relative density is the ratio of density of substance to the density of pure water at 4° C.
19. What is a hydrometer?
Ans: Hydrometer is an instrument used to measure the density of various liquid, based on the principle of flotation. There are two types of hydrometers.They are constant immersion hydrometer and constant weight hydrometer.
20. Write the application of hydrometer.
Ans: The application of hydrometer are:
         a. to measure the density of liquid.
         b. to measure the relative density of a substance.
21. What is lactometer?
Ans: An instrument that is based on law of flotation and used to measure the density of milk ( or purity) of milk is called latecomer.
22. Which device is used to measure the purity of milk?
Ans: Lactometer is used to measure the purity of milk.
23. State Pascal's law.
Ans: Pascal's law stats that "When pressure is applied in a liquid in enclosed container, the pressure is transmitted equally and perpendicularly in all directions".
24. Writ the application of Pascal’s law.
Ans: The application of Pascal's law are:
       a. Hydraulic brake       b. Hydraulic press     c. Hydraulic lift
25. The relative density of gold is 19.6. What does it mean?
Ans: It means that the gold is 19.6 times heavier than water.
26. What is the numerical value shown by hydrometer if it is sunk in pure water?
Ans: The numerical value shown by hydrometer if it is sunk in pure water is 1000kg/m3. (or
1 gm/cm3)

2 marks questions

27. Write the factors on which pressure depend. Also write their relation.
Ans: The two factors on which pressure depends on are
1.force
2. area
The relation among these factors is : p=f/A
28. Define hydraulic brake and hydraulic press.
Ans: Hydraulic brakes are the brakes which works on the principle of pascals law and are used in cars,truck.plane, etc.
Hydraulic press is a device based on pascals law it is used for pressing or compressing purpose.
29. What are the laws of liquid pressure?
Ans: The laws of liquid pressure are:
(i) Pressure inside the liquid increases with the depth from the free surface of the liquid.
(ii) Pressure is same at all points on a horizontal plane, in case of stationary liquid.
(iii) Pressure is same in all directions about a point inside the liquid.
(iv) The liquid transmits pressure equally in all direction.
(v) Pressure of liquid does not depend upon the shape of the container.
(vi) Pressure of the liquid depends upon the density of the liquid.
(vii) The liquid finds its own level.
30. What is the principle of hydraulic press?
Ans:The principle of hydraulic press are:
a. Liquids are in-compressible.
b. Liquid transmits pressure equally in all directions.
31. What are the two laws of upthrust?
Ans: The two laws of upthrust are:
      i. Upthrust is directly proportional to the volume immersed.
      ii. Upthrust is directly proportional to the density of liquid.
32. Write any two differences between force and pressure.
Ans: The differences between force and pressure are:

Force	Pressure
1. Force is an external agent that changes or tries to change the state of rest or motion of an object or it called pull or push. 2. It is the cause of pressure. 3. It does not depend on area. 4. Its SI unit is Newton(N).	1. It the force per unit area. 2. It is the effect of force. 3. It depends upon the area. 4. Its unit is Pascal (Pa).

33. Write two differences between thrust and Upthrust.
Ans: The two differences between thrust and Up-thrust are:

Thrust	Up-thrust
1. It is an external agent that change or tries to change the position, shape and direction of motion of an object. 2. It can be applied to solid, liquid and gas. 3. It is expressed as F = ma	1. It is the resultant force experience by an object when it is wholly or partially immersed in a liquid is upthrust.  2. It appears in only liquid and gas. 3. It is expressed as U = dvg.

34. Prove that P = hdg.
Ans:

By the definition of pressure,

P=FA..............(a)

P=mgA..............(b) [As, F=mg]

P=dvgA...............(c) [As, d=m/v and m = dv]

P=d(A×h)gA.........(d) [As, V=A×l]

P=dgh.........(e)  

    

Equation (e) shows that pressure exerted by liquid in a column depends on:
- density of liquid 'd'
- height of liquid column 'h'
- acceleration due to gravity 'g'
Equation (e) shows that pressure exerted by the liquid is directly proportional to the height of the liquid column, density of the liquid and acceleration due to gravity.

35. Write any two differences Archimedes' principle and Law of flotation.
Ans:

Archimedes Principle	Law of floatation
1. Archimedes' principle states that "When a body is wholly or partially immersed in liquid it experiences a loss in weight due to the upthrust which is equal to the weight of liquid displaced by it."	1. It states that floating body displaces the liquid equal to its own weight.
2. It holds true for both liquid and gas.	2. It holds true for liquid only.
3. It is applicable for both floating and sinking objects	3. It is applicable for floating objects only.

36. A balloon filled with air on the earth's surface gets burst when reaches very high from the earth's surface, why?
Ans: A balloon filled with air on the earth's surface gets burst when reaches very high from the earth's surface because of change in pressure. The atmospheric pressure decreases as balloon move higher in the atmosphere, so the internal pressure of balloon increases and becomes more than external pressure when it rises to high altitude and get burst.
37. What will be the effect in the weight of displaced water if load is added into the ship floating in the ocean? Write with reason.
Ans: The weight of displaced water will be equal to the weight of added load into the ship because the shape of ships are so designed that they will displace the water according to the added load i.e the more we add load into the ship the more will it displace the water.
38. An egg sinks in pure water but floats on concentrated solution of salt and water, why?
Ans: An egg sinks in pure water but floats on concentrated solution of salt and water because the density of salt water is more than that of pure water which results in more upthrust . The density of the egg is higher than the density of pure water so it sinks. When salt is added to the water, the saltwater solution's density becomes higher than the egg, so the egg will float.
39. Explain why a girl with high heel shoes exerts more pressure on the ground than an elephant.
Ans: A girl with high heel shoes exerts more pressure on the ground than an elephant because pressure is inversely proportional to the area, the girl with high heel shoes covers less area. So, she exerts more pressure on the ground than an elephant .
40. What is meant by upthrust and apparent loss in weight when a body is immersed in liquid?
Ans: Upthrust is the upward force that a liquid or gas exerts on a body floating in it.
Apparent loss in weight when a body is immersed in liquid means that the object displaced the amount of liquid equal to its weight due to upthrust.
41. Write down the two difference between constant immersion hydrometer and constant weight hydrometer.
Ans:

Constant immersion hydrometer	Constant weight hydrometer
1. The hydrometer which measures the density by adding the weights to immerse to the constant level.	1. The hydrometer which measure the density by observing the scale of the floating neck.
2. It gives the relative density.	2. It gives the density of a substance.

42. How does syringe help to send medicine into the body of a patient?
Ans:
43. Give reason for:
       i. A ship coming from sea enter the river with its body sinks more or less in water, why?
          Ans: The density of sea water is more than the river water. So, when ship enter
          the river it experiences less upthrust because of less density and hence its body sinks
          more in river.
       ii. Why does hydrometer have a heavy bulb and narrow stem?
          Ans: Hydrometer have heavy bulb to keep it straight up and to get correct reading.
          Similarly, it has narrow stem for greater sensitivity.
       iii. Iron nail sinks in water but a ship made up of iron floats on water, why?
            Ans: An iron nail can not displace the water equal to its weight but the ship make
            of iron can displace the water equal to its own weight and added load because of its
            shape and design. So, the iron nail sinks into water but a ship made up of iron floats
            on water.
       iv. Why the balloons are not fully inflated if they are to send into upper atmosphere?
            Ans: The atmospheric pressure at high altitude is less than at the surface of earth.
            If the balloons are fully inflated and sent into the upper atmosphere, the air pressure
            inside the balloon becomes more than the atmospheric pressure outside that cause
            the bursting of the balloons. Hence, balloons are not fully inflated if they need to
            sen into the upper atmosphere.
       v. Why it is easier to pull a bucket of water form the well until it is inside the
           water but difficult when it is outside water?
           Ans: It is easier to pull a bucket of water from the well until it is inside the water
           but difficult when it is outside the water because the weight of the bucket is less
           inside the water due to the upthrust exerted by the liquid in upward direction but
           the upthrust at the upthrust at the the bucket decrease outside  the water by which
           weight of bucket increases in the air as air has less density than water and exert
           less upthrust.
       vi. If a hydrometer is immersed in sugar solution and in pure water, in which it
            immerse more and why?
           Ans: We know that uphrust is directly proportional to density of liquid. When
           hydrometer is immersed in sugar solution it will experience more upthrust than
           the pure water because the density of sugar solution is more then pure water.
           So, hydrometer remains more immersed in pure water than sugar solution.
44. Explain, why the weight of a body is lighter in water than in air.
Ans: The density of water is more than air. We know that upthrust is directly proportional to the density, more upthrust is exerted on the object in water than in air. More upthrust iin water decreases the weight of the object. Hence, the weight of the object is more in air than in water.
45. Why is it easy to swim in salty water than in pure water?
Ans: The density of salty water is more than that of pure water. We know that, upthrust is directly proportional to the density i.e sea water exerts more upthrust than pure water. So, it is easier to swim in sea water than in pond water.
46. Why does a ball of iron sink in water while a ship made of iron can float in water?
Ans: A ball or iron sinks in water but a ship made of iron can float in water. According to the principle of flotation, when the weight of the water displaced by a body is equal to the weight of the body, then it floats. Ships are so shaped that they are capable of displacing water equal to their won weight and added load on it. If extra load is added, the ship sinks deeper, so that additional water displaced has weight equal to the load.

3 marks questions

47. Prove that hydraulic lift help to multiply the effort applied.
                                            Or
      Hydraulic machine is a force multiplier. Prove it
Ans: Let us consider a hydraulic press filled with water and fitted with air pistons P1 and P2 with cross-section area A1 and A2 respectively. Here, area A1 is smaller than area A2.
When force F1 is applied on a small piston in downward direction , it produces force F2 on piston P2 which moves upward direction due to equal transmission of pressure in all direction according to Pascal’s law.
According to Pascal’s law,
Pressure on small cylinder with piston P1 = Pressure on big cylinder with piston P2.
So, P1 = P2
Where P1 and P2 are pressure on small and big piston.

Or, F1A1=F2A2

Or, F2=F1×A2A1

Since, A₂ >A₁ then F­₂ >F₁.

Therefore, hydraulic press or hydraulic lift acts as force multiplier. 48. Prove by an activity that atmosphere exerts pressure.
48. Density of three unknown substances are given in the table:

      i. Which one will have the least volume if equal mass of three
         are taken?
      ii. Which one floats on water? Why?
      iii. Among them which two will sink in water?
Ans: i. Substance 'x' will have the least volume if equal mass of three are taken because volume of a body is inversely proportional to the density of the object i.e the higher the density the lower will be the volume.
ii. Substance 'z' will float on water barbecue the density of 'z' is less than that of water.
iii. Substance 'x' and 'y' will sink in water because they have density greater than that of water.
50. Write three differences between Archimedes principle and Law of flotation.
Ans:
51. Write three differences Density and relative density.
Ans:

Density	Relative density
1. It is the mass per unit volume.	1. It is the ratio of density of a substance to the density of water at 4°C.
2. It can be expressed as: $D=\frac{m}{v}$	2. It can be expressed as: $R.D=\frac{\text{Density of substance}}{\text{density of water at 4}{}^\circ \text{C}}$
3. Its SI unit is kg/ m3.	3. It has no unit.

52. The different weight of a piece of stone on weighing in three different media air, water and salt
      solution are given in the tale below. Answer the following questions:

      i. Identify media A, B and C.
      ii. If the weight of 1 kg of mass in air is 10N, what is the mass of the piece of stone?
      iii. Find out the mass of water displaced by the piece of stone.
Ans: i. Out of three media A is salt solution, B is air and c is water.
ii.
53. Prove that U = vdg or U = mg or U = Adg(h₂ – h₁)

54. Explain the up stroke and down stroke of water pump.

55. Experimentally prove that up thrust is equal to the weight of liquid displaced.

56. The figure shows a small iron ball sunk in a beaker of fresh water. Now, if some table salt is
      added to the water in the beaker, explain how the up-thrust experienced by the ball will be
      affected?

57. Mention the relationship between the density of liquid and up-thrust. In the given diagram, an
      object ABCD is shown dipped in liquid, on which surface the pressure is greater in AB surface or
      in CD surface? Why?

58. In the diagram, if the area of piston A is 0.05 m² and that of B is 0.15 m² .What force is produced
      in B when 20 N force is applied in piston A

59. The three objects X, Y and Z with different densities are placed in water inside a beaker as shown
      in the figure. Answer the following questions:

      i. Which object has higher density than water?
      ii. If the mass of object A is 1 Kg. How much kilogram of water is displaced by the object?
      iii. Which law is applicable for object B? State it.

4 marks questions 

61. Study the diagram and answer the following questions:

       i. What is the weight on an object in the air?
       ii. How much up-thrust is exerted by liquid on that object?
       iii. Calculate the mass of the object.
       iv. State the law on which this experiment is based.
62. In the figure, calculate the following:

       i. The pressure at P
       ii. The pressure at Q
       iii. The force on the piston Q.
63. The figure shows a hydrometer floating in fresh water. 2 cm of the stem of the hydrometer is
      outside the water. Study the diagram and answer the following questions:

      a. What is the function of the hydrometer?
      b. If the weight of the hydrometer shown in the diagram is 0.2 N, how much is the up-thrust of
          water on the bulb of the hydrometer?
      c. What will happen if the fresh water is replaced by salt water?
64. Study the figure and answer the following:

     a. What is the weight of an object in the air?
     b. How much up-thrust is exerted by liquid on that object?
     c. Calculate the mass of the object.
     d. State the law on which this experiment is based. 

65. How does water pump help to pump water from well? Explain with diagram.

Numerical