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64. What is the velocity v of a metallic ball of radius r falling in a tank of liquid at the instant when its acceleration is one-half that of a freely falling body ?

(The densities of metal and of liquid are ρ and σ respectively, and the viscosity of the liquid is η). (a) [(r2g)/(9η)][ ρ -2σ] (b) [(r2g)/(9η)][ 2ρ -σ] (c) [(r2g)/(9η)][ ρ -σ] …

63. A manometer connected to a closed tap reads

4.5×105 pascal. When the tap is opened the reading of the manometer falls to 4×105 pascal. Then the velocity of flow of water is (a) 7 m/s …

3. The diagram shows a cup of tea seen from above. The tea has been stirred and is now rotating without turbulence. A graph showing the speed v with which the liquid is crossing points at a distance X from O along a radius XO would look like

Answer-d (7)

45. A streamlined body falls through air from a height h on the surface of a liquid. If d and D(D > d) represents the densities of the material of the body and liquid respectively, then the time after which the body will be instantaneously at rest, is

(a) √2h/g (b) √(2hD)/gd (c) √(2hd)/gD (d) …

44. A rectangular vessel when full of water takes 10 minutes to be emptied through an orifice in its bottom. How much time will it take to be emptied when half filled with water

(a) 9 minute (b) 7 minute (c) 5 minute (d) 3 minute Answer-b (3)

52. A small drop of water falls from rest through a large height h in air; the final velocity is

(a) ∝ √h (b) ∝ h (c) ∝ (1/h) (d) Almost independent of h Answer-d (11)

49. The coefficient of viscosity for hot air is

(a) Greater than the coefficient of viscosity for cold air (b) Smaller than the coefficient of viscosity for cold air (c) Same as the coefficient of viscosity for cold air (d) Increases or decreases depending on the external pressure Answer-a …

48. As the temperature of water increases, its viscosity

(a) Remains unchanged (b) Decreases (c) Increases (d) Increases or decreases depending on the external pressure Answer-b (7)

46. A large tank is filled with water to a height A small hole is made at the base of the tank. It takes time

T1 to decrease the height of water to H/η (η>1) ; and it takes T2 time to take out the rest of water. If T1 =T2, then the value of η is (a) 2 (b) 3 (c) 4 (d) 2√2 Answer-c …

47. Velocity of water in a river is

(a) Same everywhere (b) More in the middle and less near its banks (c) Less in the middle and more near its banks (d) Increase from one bank to other bank Answer-b (8)

62. Water falls from a tap, down the streamline

(a) Area decreases (b) Area increases (c) Velocity remains same (d) Area remains same Answer-a (27)

61. When a body falls in air, the resistance of air depends to a great extent on the shape of the body, 3 different shapes are given. Identify the combination of air resistances which truly represents the physical situation. (The cross sectional areas are the same).

(a) 1 < 2 < 3 (b) 2 < 3 < 1 (c) 3 < 2 < 1 (d) 3 < 1 < 2 Explanation- (c) A stream lined body has less resistance due to air. (15)

60. Two capillary of length L and 2L and of radius R and 2R are connected in series. The net rate of flow of fluid through them will be

(given rate of the flow through single capillary, X=(Π PR4)/ηL (a) (8/9)X (b) (9/8)X (c) (5/7)X …

59. Water is flowing in a pipe of diameter 4 cm with a velocity 3 m/s. The water then enters into a tube of diameter 2 cm. The velocity of water in the other pipe is

(a) 3 m/s (b) 6 m/s (c) 12 m/s (d) 8 m/s Answer-c (9)

58. A viscous fluid is flowing through a cylindrical tube. The velocity distribution of the fluid is best represented by the diagram

Answer-c (253)

57. Water flows in a streamlined manner through a capillary tube of radius a, the pressure difference being P and the rate of flow Q. If the radius is reduced to a/2 and the pressure increased to 2P, the rate of flow becomes

(a) 4 Q (b) Q (c) Q/4 …

56. Two capillaries of same length and radii in the ratio 1 : 2 are connected in series. A liquid flows through them in streamlined condition. If the pressure across the two extreme ends of the combination is 1 m of water, the pressure difference across first capillary is

(a) 9.4 m (b) 4.9 m (c) 0.49 m (d) 0.94 m Answer-d (13)

55. Two capillary tubes of the same length but different radii

r1 and r2 are fitted in parallel to the bottom of a vessel. The pressure head is P. What should be the radius of a single tube that can replace the two tubes so that the rate of flow is …

54. In Poiseuilli’s method of determination of coefficient of viscosity, the physical quantity that requires greater accuracy in measurement is

(a) Pressure difference (b) Volume of the liquid collected (c) Length of the capillary tube (d) Inner radius of the capillary tube Answer-d (6)

53. The rate of flow of liquid in a tube of radius r, length l, whose ends are maintained at a pressure difference P is

V=(πQPr4) /ηl where η is coefficient of the viscosity and Q is (a) 8 (b) 1/8 (c) 16 (d) 1/16 Answer-b (15)

51. We have three beakers A, B and C containing glycerine, water and kerosene respectively. They are stirred vigorously and placed on a table. The liquid which comes to rest at the earliest is

(a) Glycerine (b) Water (c) Kerosene (d) All of them at the same time Answer-a (8)

50. A good lubricant should have

(a) High viscosity (b) Low viscosity (c) Moderate viscosity (d) High density Answer-a (6)

24. In a turbulent flow, the velocity of the liquid molecules in contact with the walls of the tube is

(a) Zero (b) Maximum (c) Equal to critical velocity (d) May have any value Answer-d (2)

43. A cylindrical vessel of 90 cm height is kept filled upto the brim. It has four holes 1, 2, 3, 4 which are respectively at heights of 20 cm, 30 cm, 45 cm and 50 cm from the horizontal floor PQ. The water falling at the maximum horizontal distance from the vessel comes from

(a) Hole number 4 (b) Hole number 3 (c) Hole number 2 (d) Hole number 1 Answer-b (8)

42. A tank is filled with water up to a height H. Water is allowed to come out of a hole P in one of the walls at a depth D below the surface of water. Express the horizontal distance x in terms of H and D

(a) x=√D(H-D) (b) x=√[D(H-D)]/2 (c) x=2√D(H-D) (d) x=4√D(H-D) Answer-c (3)

41. An L-shaped glass tube is just immersed in flowing water such that its opening is pointing against flowing water. If the speed of water current is v, then

(a) The water in the tube rises to height v2 /2g (b) The water in the tube rises to height g/2v2 (c) The water in the tube does not rise at all (d) None of these Answer-a (71)

40. Fig. represents vertical sections of four wings moving horizontally in air. In which case the force is upwards

Answer-a (22)

39. An L-shaped tube with a small orifice is held in a water stream as shown in fig. The upper end of the tube is 10.6 cm above the surface of water. What will be the height of the jet of water coming from the orifice? Velocity of water stream is 2.45 m/s

(a) Zero (b) 20.0 cm (c) 10.6 cm (d) 40.0 cm Answer-b (9)

38. sniper fires a rifle bullet into a gasoline tank making a hole 53.0 m below the surface of gasoline. The tank was sealed at 3.10 atm. The stored gasoline has a density of

660 kgm–3. The velocity with which gasoline begins to shoot out of the hole is (a) 27.8 m/s (b) 41.0 m/s (c) 9.6 m/s (d) 19.7 m/s Answer-b …

37. A liquid flows through a horizontal tube. The velocities of the liquid in the two sections, which have areas of cross-section

A1 and A2 , are v1 and v2 The difference in the levels of the liquid in the two vertical tubes is h (a) The volume of the liquid flowing through the tube in unit time is A1v1 (b) v2 …

36. In this figure, an ideal liquid flows through the tube, which is of uniform cross-section. The liquid has velocities

vA and vB , and pressure PA and PB at points A and B respectively (a) vA = vB (b) vB > vA (c) PA = PB (d) PB > PA Answer- a,d (164)

34. At what speed the velocity head of a stream of water be equal to 40 cm of Hg

(a) 282.8 cm/sec (b) 432.6 cm/sec (c) 632.6 cm/sec (d) 832.6 cm/sec Answer-a (9)

35. The weight of an aeroplane flying in air is balanced by

(a) Upthrust of the air which will be equal to the weight of the air having the same volume as the plane (b) Force due to the pressure difference between the upper and lower surfaces of the wings, created by …

33. According to Bernoulli’s equation

[P/(ρg)]+ h + (1/2)(v2/g) The terms A, B and C are generally called respectively: (a) Gravitational head, pressure head and velocity head (b) Gravity, gravitational head and velocity head (c) Pressure head, gravitational head and velocity head (d) Gravity, pressure …

32. The pans of a physical balance are in equilibrium. Air is blown under the right hand pan; then the right hand pan will

(a) Move up (b) Move down (c) Move erratically (d) Remain at the same level Answer-b (18)

27. Water is flowing through a horizontal pipe of non-uniform cross-section. At the extreme narrow portion of the pipe, the water will have

(a) Maximum speed and least pressure (b) Maximum pressure and least speed (c) Both pressure and speed maximum (d) Both pressure and speed least Answer-a (4)

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