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19. A ball of radius r and density ρ falls freely under gravity through a distance h before entering water. Velocity of ball does not change even on entering water. If viscosity of water is η, the value of h is given by

(a)  (2/9)r2[(1- ρ)/η]g (b)    (2/81)r2[(ρ- 1)/η]g (c)    (2/81)r4[(ρ- 1)/η]2 g (d)    (2/9)r4[(ρ- 1)/η]2 g Answer-c (8)

27. The work done in increasing the size of a soap film from

10 cm× 6 cm to 10 cm × 11 cm is 3 ×10-4 joule. The surface tension of the film...

18. A rectangular block is 5 cm × 5 cm × 10cm in size. The block is floating in water with 5 cm side vertical. If it floats with 10 cm side vertical, what change will occur in the level of water?

(a)  No change (b)   It will rise (c)   It will fall (d)   It may rise or fall depending on the...

6. A liquid is coming out from a vertical tube. The relation between the weight of the drop W, surface tension of the liquid T and radius of the tube r is given by, if the angle of contact is zero

(a)  w= πr2T (b) w= 2πrT (c)w= 2πr2T (d) w= (3/4)πr3 T Ans. b (5)

7. The parts of motor cars are polished by chromium because the angle of contact between water and chromium is

(a)      0o      (b)   90o (c)   Less than 90o                               (d)  Greater than 90o Ans. d (5)

17. A small sphere of mass m is dropped from a great height. After it has fallen 100 m, it has attained its terminal velocity and continues to fall at that speed. The work done by air friction against the sphere during the first 100 m of fall is

(a) Greater than the work done by air friction in the second 100 m (b)  Less than the work done...

16. Spherical balls of radius ‘r’ are falling in a viscous fluid of viscosity

‘η‘ with a velocity ‘v‘. The retarding viscous force acting on the spherical ball is (a) Inversely proportional to ‘r‘...

15. A square plate of 0.1 m side moves parallel to a second plate with a velocity of 0.1 m/s, both plates being immersed in water. If the viscous force is 0.002 N and the coefficient of viscosity is 0.01 poise, distance between the plates in m is

(a)  0.1                                     ...

13. A cylindrical tank has a hole of 1 cm2 in its bottom. If the water is allowed to flow into the tank from a tube above it at the rate of

70 cm3/sec. then the maximum height up to which water can rise in the tank is (a)   2.5 cm                                        (b) ...

13. There is a hole of area A at the bottom of cylindrical vessel. Water is filled up to a height h and water flows out in t second. If water is filled to a height 4h, it will flow out in time equal to

(a)   t                                     ...

12. There is a hole in the bottom of tank having water. If total pressure at bottom is 3 atm

(1 atm = 105N/m2) then the velocity of water flowing from hole is (a)  √400 m/s            ...

11. A cylinder of height 20 m is completely filled with water. The velocity of efflux of water (in m/s) through a small hole on the side wall of the cylinder near its bottom is

(a)      10                                  (b)  20...

10. A large tank filled with water to a height ‘h’ is to be emptied through a small hole at the bottom. The ratio of time taken for the level of water to fall from h to h/2 and from h/2 to zero is

(a) √2                                  (b) 1/...

8. A manometer connected to a closed tap reads

3.5 × 105 N/m2. When the valve is opened, the reading of manometer falls to 3.0 × 105 N/m2, then...

10. The radius of a soap bubble is increased

from (1/√π) cm to (2/√π) cm. If the surface tension of water is 30 dynes per cm, then the work done...

5. Water is moving with a speed of

5.18 ms–1 through a pipe with a cross-sectional area of 4.20 cm2. The water gradually descends 9.66 m as the...

5. Radius of a soap bubble is ‘r’, surface tension of soap solution is T. Then without increasing the temperature, how much energy will be needed to double its radius

(a)    4πr2T (b) 2 πr2T (c) 12 πr2T (d) 24 πr2T Ans. d (54)

10. Air is streaming past a horizontal air plane wing such that its speed in 120 m/s over the upper surface and 90 m/s at the lower surface. If the density of air is 1.3

kg per metre3 and the wing is 10 m long and has an average width of 2 m, then the...

16. If the surface tension of a liquid is T, the gain in surface energy for an increase in liquid surface by A is

(a) AT-1 (b) AT (c)  A2T (d) A2T2 Ans. b (6)

15. If two identical mercury drops are combined to form a single drop, then its temperature will

(a)  Decrease (b)  Increase (c)  Remains the same (d)  None of the above Ans. b (4)

14. The work done in blowing a soap bubble of radius r of the solution of surface tension T will be

(a)  8πr2T (b) 2πr2T (c)  4πr2T (d) (4/3)πr2T Ans. a (6)

13. A spherical drop of oil of radius 1 cm is broken into 1000 droplets of equal radii. If the surface tension of oil is 50 dynes/cm, the work done is

(a)  18 π ergs (b)  180 π ergs (c)  1800 π ergs (d)  8000 π ergs Ans. c (6)

12. If work W is done in blowing a bubble of radius R from a soap solution, then the work done in blowing a bubble of radius 2R from the same solution is

(a)  W/2 (b)  2W (c)   4W (d) (7/3) W Ans. c (33)

11. The surface tension of a liquid is 5 N/m. If a thin film of the area 0.02 m2 is formed on a loop, then its surface energy will be

(a)    5 x 102 j (b)  2.5  x 10-2 j (c)    2 x 10-1 (d)  5 x 10-1 j...

9. If T is the surface tension of soap solution, the amount of work done in blowing a soap bubble from a diameter D to 2D is

(a)  2  πD2T (b)  4 πD2T (c)   6  πD2T (d)  8 πD2T Ans. c (11)

8. The amount of work done in blowing a soap bubble such that its diameter increases from d to D is (T= surface tension of the solution)

(a) 4π(D2-d2)T (b) 8π(D2-d2)T (c) π(D2-d2)T (d) 2π(D2-d2)T Ans. d (8)

7. A spherical liquid drop of radius R is divided into eight equal droplets. If surface tension is T, then the work done in this process will be

(a)  2  πR2T (b)  3 πR2T (c)  4  πR2T (d)  2 πR2T Ans. c (32)

7. In the following fig. is shown the flow of liquid through a horizontal pipe. Three tubes A, B and C are connected to the pipe. The radii of the tubes A, B and C at the junction are respectively 2 cm, 1 cm and 2 cm. It can be said that the

(a)  Height of the liquid in the tube A is maximum (b)   Height of the liquid in the tubes A...

6. The velocity of kerosene oil in a horizontal pipe is 5 m/s.

If  g=10 m/s2 then the velocity head of oil will be (a)   1.25 m                                             (b)   12.5 m (c)   0.125 m ...

1. Energy needed in breaking a drop of radius R into n drops of radii r is given by

(a) 4πT(nr2-R2) (b) (4/3)π(r3n-R2) (c)  4πT(R2-nr2) (d) 4πT(nr 2 + R2) Ans.a (5)

2. The potential energy of a molecule on the surface of liquid compared to one inside the liquid is

(a)  Zero (b)  Smaller (c)   The same (d)  Greater Ans. d (9)

3. Two droplets merge with each other and forms a large droplet. In this process

(a)  Energy is liberated (b)  Energy is absorbed (c)   Neither liberated nor absorbed (d)  Some mass is converted into energy...

4. A drop of liquid of diameter 2.8 mm breaks up into 125 identical drops. The change in energy is nearly (S.T. of liquid =75 dynes/cm)

(a)  Zero (b)  19 erg (c)   46 erg (d)  74 erg Ans. d (4)

20. Two solids A and B float in water. It is observed that A floats with 1/2 of its body immersed in water and B floats with 1/4 of its volume above the water level. The ratio of the density of A to that of B is

(a)    4 : 3                               ...

19. A ball whose density is

0.4 × 103 kg/m3 falls into water from a height of 9 cm . To what depth does the ball...

17. A hollow sphere of volume V is floating on water surface with half immersed in it. What should be the minimum volume of water poured inside the sphere so that the sphere now sinks into the water

(a)   v/2                                     ...

16. If the surface of a liquid is plane, then the angle of contact of the liquid with the walls of container is

(a)  Acute angle (b)  Obtuse angle (c)  90° (d)  0° Ans. (d) Tangent drawn at point of contact makes 0°...

15. For which of the two pairs, the angle of contact is same

(a)  Water and glass; glass and mercury (b) Pure water and glass; glass and alcohol (c)   Silver and water; mercury...

14. What is the shape when a non-wetting liquid is placed in a capillary tube

(a)  Concave upward (b)  Convex upward (c)  Concave downward (d)  Convex downward Ans. (b) Since for such liquid (Non-wetting) angle...

13. A liquid wets a solid completely. The meniscus of the liquid in a sufficiently long tube is

(a)  Flat (b)  Concave (c)   Convex (d)  Cylindrical Ans. b (7)

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