| Previous Year Questions of March Examinations from 2010 to 2020 |
| Chapter Name: MECHANICAL PROPERTIES OF FLUIDS |
|
Washing with water doesn’t remove grease stains from clothes but addition of detergent removes the molecules of greasy substances. a) Which property of a liquid causes the above effect? b) A single drop of liquid is split into 8 identical drops. What will be the excess pressure in each drop? c) How can the coefficient of viscosity of a highly viscous liquid the determined by Stokes method? |
|
a) Elasticity is an internal property of matter. Fluids possess volume elasticity. Which is more elastic, air or water? Why? b) Hydraulic lift is a device used to lift heavy loads. State the principle behind the working of this device. c) The velocity of outflow of a liquid from an open tank is identical to that of a freely falling body. i.Name this law and the principle behind this law. ii. Derive this law based on this principle. |
|
a) A solid sphere falling through a viscous medium attains a constant velocity called terminal velocity after some time of its fall. What are the different forces acting on the sphere? Derive an expression for terminal velocity in terms of the coefficient of viscosity of the medium. b) Water kept in earthern pots gets cooled. Why? |
Match the following:
|
|
Raindrops falling due to gravity do not acquire high velocity. a) Define the velocity of the raindrop when unbalanced force on it is zero. b) Why do bubbles of air rise up through water? c) The terminal velocity of copper ball of radius 2.0 mm falling through a tank of oil at 200C is 6.5cm s -1 . Compute the viscosity of the oil at 200C. Density of oil is 1.5 x 10 3 kgm -3 density of copper is 8.9 x 103 kg m -3 . d) Viscosity of gases........with temperature, whereas viscosity of liquids .........with temperature (increases/decreases). |
|
A small water drop placed on a lotus leaf is spherical in shape. a) Define surface tension. b) Why does the small water drop acquire a spherical shape? |
| Three vessels of different shapes are filled with water to the same height ‘h’ and their bottom parts are connected to manometers measuring the pressure. The water levels in all the vessels remaining the same. a) Identity the above phenomenon. b) Predict the pressure level shown by the manometers. c) Blood pressure in humans is greater at the feet than at the brain. Explain why. d) Pick the odd one out. Dentist chair, hydraulic brake, hydraulic press, venture meter. |
 |
| The flow of an ideal fluid in a pipe of varying cross section is shown. a) Differentiate between streamline flow and turbulent flow. b) State and prove Bernoulli’s principle. |
 |
|
Fill in the blanks. Venturimeter : Bernoulli’s theorem Hydraulic lift : .................... |
| The figure shows the pressure – volume relationship of an ideal gas that undergoes a Carnot cycle. The process B to C takes place at a constant temperature of 1000 K and the process from D to A at a constant temperature of 500 K. (a) Name the process occurring between i) A and B ii) B and C b)During which of the four processes, is work done by the gas? (c) How can you find the total work done during a cycle from the graph? (d) Calculate the efficiency of the cycle. |
 |
| The viscous force exists when there is a relative motion between the layers of the fluid. a) State true or false: “The viscosity of gases decreases with an increase in temperature.” b) Obtain the expression for the terminal velocity attained by an object falling through a viscous medium. c) The speed – time graph of a falling sky diver is shown below. During the fall he opens his parachute. Which part of the graph shows the sky diver falling with terminal velocity? |
 |
| There is always an excess of pressure inside drops and bubbles. a) State true or false: “A drop of liquid under no external forces is always spherical in shape.” b) Obtain an expression for excess of pressure inside a drop of radius r and surface tension S. c) Two soap bubbles A and B are blown at the ends of a tube, as shown below. Choose the correct answer: When the block C is removed... i. The size of A increases and that of B decreases ii. The size of B increases and that of A decreases iii. No change occurs in their sizes iv. Their sizes become equal |
 |
| The antiseptic used for cuts and wounds in human flesh have low surface tension. Due to low surface tension, they spread over the wounds easily. a) In the following figure, the angle of contact θ is......… b) Surface tension causes capillarity. Define capillarity and arrive at the expression for capillary rise in terms of surface tension. c) In a capillary tube, water rises to a height. If the capillary tube is inclined at an angle 600 with the vertical, what will be the length of the water column in the tube. |
 |
| The pressure of the atmosphere at any point is the weight of the air column of a unit cross sectional area. Its unit is bar. a) Identify the given diagram and write its use. b) State Pascal’s law for transmission of fluid pressure and explain the principles of working of a hydraulic lift. c) The above arrangement is placed in an elevator which is accelerating upwards. What happens to the possible height of the liquid column in the tube? Justify. |
 |
|
In case of fluids law of conservation of energy can be explained with Bernoulli’s principle. a) State and prove Bernoulli’s principle. b) While travelling in aeroplane, it is advisable to remove ink from fountain pen. Why? |
|
Viscosity is the frictional force in fluids. a) When a small metal ball is falling through a viscus medium, what are the various forces acting on it? Using this arrive at an expression for terminal velocity. b) Raindrops falling under gravity do not acquire very high velocity. Why? |
| Draw the schematic diagram of a hydraulic lift. Give its working principle |
| Graph given exhibits the anomalous expansion of water. Based on the graph, explain how lakes freeze frorm the top to bottom rather than from bottom to top |
 |
| Regiion of streamline flow of an incompressible floud is shown in the figure. a) By considering mass conservation in the fluid flow arrive at the “equation of continuity”. b) The onset of turbulence in a fluid is determined by “Reynold number”, RE = ......... i) ρ v d / 2η ii) 2 ρ v d / η iii) ρ v d / η iv) ρ v m / d |
 |
| Schematic diagram of capillary rise in a narrow tube is shown in the figure. a) Arrive an expression for catillary height “h” in terms of the surface tension of the liquid b) On the surface of the moon, the liquid in a capilary tube will rise to the ........... i) same height on earth ii) less height on earth iii) more height than on earth iv) infinite height |
 |
| The terminal velocity of a copper ball of radius 2.0 mm falling through a tank of oil at 20°C is 6.5 cm / s. Calculate the viscosity of the oil at 20°C. (Hints : Density of oil is 1.5 x 103 kg m-3, density of copper is 8.9 x103 kg m-3) |
| A device used to lift automobiles is shown in the figure a) Write the name of the device b) In the situation shown in the figure, mass of the car is 3000 kg and area of the piston carrying it is 425 cm2. What pressure is to be applied to the smaller piston? |
 |
|
a) Water rises up in a narrow tube in spite of gravity. This phenomenon is called ....... b) Derive an expression for the height of water in the tube in terms of radius of the tube and surface tension of the liquid c) Water with detergent dissolved in it should have ....................... (small/large) angle of contact |
|
a) Define angle of contact b) Water proofing agents are added to create a ......... (large / small) angle of contact between the water and fibres c) Calculate the excess of pressure inside an air bubble of radius 1 mm formed just below the free surface of water. Given surface tension of water 72 x 10 -3 Nm-1 |
| a) Derive Bernoulli"s equation for the stream line flow of an incompressible liquid b) Figures (a) and (b) refer to the steady flow of a (non viscous) liquid. Which one of the given two figures is INCORRECT |
 |
| The given figure shows the principle behind the hydraulic lift. The radius of small piston is 5.0 cm and that of larger piston is 15 cm. Calculate the force F, if the mass of the car to be lifted is 1350 kg (g = 9.8 ms –2 ). |
 |
| What do you mean by capillary rise ? What is the phenomenon responsible for it ? |
| Consider a fluid moving in a pipe of varying cross-sectional area as shown in figure. a1 , a2 are cross-sectional areas of pipe and v1 , v2 are the velocities of fluid. (a) State Bernoulli’s principle. (b) Derive Bernoulli’s equation. (c) Write the equation of Stoke’s law. |
 |