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Tuesday, 30 June 2015

Pressure notes

Sharmasir …........9718041826
Pressure : The thrust (force) acting normally on unit area of a surface is called pressure.

SI unit of pressure is newton/(metre)2 or N/m2. It is commonly called pascal (Pa).Definition of pascal : When a force of 1 newton acts normally on an area of cross-section 1 m2, then the pressure experienced by the surface is said to one pascal.

Buoyancy : The phenomenon due to which a body on being immersed in a fluid experiences an upward force is called buoyancy.

Buoyant force or upthrust : The upward force experienced by a body on being immersed in a fluid is called buoyant force or upthrust.

Buoyant force or upthrust acting on a body is always equal to the weight of the fluid displaced by the immersed part of the body in the fluid.
Archimedes’ Principle : When a body is partially or wholly immersed in a fluid, it experiences an upthrust (or apparently loses its weight) which is equal to the weight of the fluid displaced by the immersed part of the body. 

 Density : Mass per unit volume of a substance is called density. Its unit in CGS system is g/cm3 and in SI system is kg/m3.

Relative density : The ratio between the density of a substance and the density of water at 4°C is called relative density. The relative density is a pure number and has no units.
.Important questions 

1.Give reason why, a block of plastic when released under water comes up to the surface of water.

 2.Define density. What is the SI unit of density
3.Name and define SI unit of pressure.

4.What do you understand by the term buoyancy?

5.Why does a mug full of water feel lighter inside water?

6.A perpendicular force of 50 N acting on a surface generates a pressure of 250 Pa. Calculate the area of cross-section of the surface on which pressure is acting.

7.What is a lactometer used for?
8.State the unit of density and relative density in SI system.

9.State Archimedes’ principle.

10.What is meant by buoyant force?

11.A cork floats while the nail sinks in water. Give reason.

12.What is the principle of flotation?

13.A body of mass 400 g has a volume of 300 cm3. Will body sink in water or not? [Density of water = 1000 kgm–3]
  1. When we stand on loose sand, our feet go deep into the sand. But when we lie down on the sand our body does not go that deep in the sand. Why?
  2. Define relative density of a substance. Relative density of silver is 10.8. The density of water is 1000 kgm–3. What is the density of silver in SI units?
  3. A cork floats in water, while the iron nail sinks. Give reason.
  4. State Archimedes’ Principle. Based on this principle, write its two applications.
  5. (i) Define pressure. (ii) Why is it easy to walk on sand with flat shoes, then with high heel shoes?
  6. (i) Define buoyant force. (ii) Mention any two factors affecting the buoyant force
  7. Loaded test-tube placed in pure milk sinks to a certain mark (M). Now some water is mixed with the milk. Will the test tube sink more or less? Explain.
  8. If two equal weights of unequal volumes are balanced in air, what will happen when these are completely dipped in water?
  9. The volume of 40 g of a solid is 15 cm3. If the density of water is 1 g/cm3, will the solid float or sink? Why?
    Sharmasir …........9718041826
  10. A steel needle sinks in water but a steel ship floats. Explain how.
  11. (a) Name the forces acting on a body? When it is fully or partially immersed in a liquid. (b) Briefly explain, why some objects float and some sink?
  12. A dining hall has dimension 50 m × 15 m × 3.5 m. Calculate the mass of air in the hall. (Given, density of air = 1.30 kg/m3)
  13. Relative densities of two substances A and B are 2.5 and 0.9 respectively. Find densities of A and B. Also find whether they will sink or float in water. (Density of water = 1000 kg/m3)
  14. (a) List two factors on which buoyant force depends. (b) Find pressure, when a thrust of 20 N is applied on a surface area of 10 cm2.
  15. Which will exert more pressure 100 kg mass on 10 m2 or 50 kg mass on 5 m2? Give reason.
  16. (a) Explain why a truck or a motor bus has much wider tyres? (b) Why do we feel lighter when we swim?
  17. You have a bag of cotton and an iron bar, each indicating a mass of a 100 kg when measure on a weighing machine. In reality, one is heavier than the other. Can you say which one is heavier and why?
  18. Account for the statement : ‘‘camel walks easily on sand but it is difficult for a man to walk on sand though a camel is much heavier than a man’’
  19. A piece of stone is tied at one end of a rubber string and holding from other end, it is allowed to immersed partially then full into water. What difference if any, you will observe, and why?
  20. An object of 40 N weight when immersed in water losses 10 N weight. Will the object float or sink? Why?
  21. Why is it easier to swim in sea water than in river water?
  22. Differentiate between density and relative density?
  23. What is Thrust? Why do buildings have wide foundation?
  24. . Lead has greater density than iron and both are denser than water. Is the buoyant force on a lead object greater than, or lesser than or equal to
    1. The wheels of a army tank rest on a steel belt, give reason.
    2. 26. While drawing water from a well, a bucket of water appears to be heavier as it comes out of the water. Explain giving reasons.
    3. Why are railway tracks laid on large sized concrete sleepers? Explain.
    4. What happens when : (a) Buoyant Force exerted by the fluid is less than the weight of the body? (b) Buoyant Force exerted by the fluid is equal to the weight of the body?
    5. What is Relative Density? The relative density of a substance is greater than 1, what does it signify?
    6. If relative density of aluminium is 2.7 and density of water is 1000 kg/m3. What is the density of aluminium in SI unit?
    7. The volume of a solid block is 300 cm3, find the mass of water displaced when it is immersed in water? (Density of water is 1 g/cm3)
    8. . A solid object of mass 50 g and volume 100 cm3 is put in water. Will the object float or sink? Give reasons for your answer.
    9. Name the instrument used to determine the density of liquid in which balance and graduated cylinder are not required. Why this instrument is made heavy near the bottom?
    10. A sphere of mass 5 kg and volume 2.2 × 10–4 m3 is completely immersed in water. Find the buoyant force exerted by water on the sphere. Density of water = 1000 kgm–3. (Given : g = 9.8 ms–2
      )Sharmasir …........9718041826
    11. . A ship is loaded in sea water to maximum capacity. What will happen if this ship is moved to river water? Why?
    12. (a) Differentiate between upthrust and weight. (b) When does an object float or sink?
    13. . A sealed can of mass 600 g has a volume of 500 cm3. Will this can sink or float in water? [Density of water is 1 gcm–3] Why?
    14. Explain the factors which determine whether an object floats or sinks when placed on the surface of water.
    15. Two blocks, one of iron and other of wood are immersed in water at same depth. Which one will come upward?
    16. (a) Define relative density. (b) If the relative density of a substance is less than 1, will it float or sink in water support your answer? (Density of water = 1000 kg m3)
    17. (a) Define relative density. (b) Relative density of gold is 19.3. The density of water is 10.3 kg/m3. What is the density of gold in S.I. Units?
    18. The mass of an empty 40 litre petrol tank of a vehicle is 8.0 kg. What will be its mass when filled completely with a fuel of density 700 kg/m3.
    19. (a) A floating boat displaces water weighing 6000 N. (i) What is the buoyant force on the boat? (ii) What is the weight of boat? (b) What happens to the buoyant force as more and more volume of a solid object is immersed in a liquid?
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