PhysicsFlame Institute

5. Assertion : A man sitting in a boat which is floating on a pond. If the man drinks some water from the pond, the level of the water in the pond decreases. Reason : According to Archimede’s principle the weight displaced by body is equal to the weight of the body.

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion. (b) If both assertion and reason are true but reason is not the correct explanation of the assertion. (c) If assertion is …

4. Assertion : To float, a body must displace liquid whose weight is greater than the actual weight of the body. Reason : The body will experiences no net downward force, in the case of floating.

3. Assertion : Hydrostatic pressure is a vector quantity. Reason : Pressure is force divided by area, and force is a vector quantity.

2. Assertion : The blood pressure in humans is greater at the feet than at the brain. Reason : Pressure of liquid at any point is proportional to height, density of liquid and acceleration due to gravity.

1. Assertion : Pascal law is the working principle of a hydraulic lift. Reason : Pressure is equal to thrust per area.

5. From amongst the following curves, which one shows the variation of the velocity v with time t for a small sized spherical body falling vertically in a long column of a viscous liquid

Answer-d (99)

66. An incompressible fluid flows steadily through a cylindrical pipe which has radius 2r at point A and radius r at B further along the flow direction. If the velocity at point A is v, its velocity at point B is

(a) 2v (b) v (c) v/2 (d) 4v Answer-d (5)

25. Assertion : Terminal velocity is same as the critical velocity. Reason : The constant velocity of fall of a body through a viscous fluid is called terminal velocity.

24. Assertion : To empty an oil tank, two holes are made. Reason : Oil will come out two holes so it will emptied faster.

23. Assertion : It is difficult to stop bleeding from a cut in the body at high altitudes. Reason : The atmospheric pressure at high altitude is lesser than the blood pressure.

22. Assertion : Railways tracks are laid on small sized wooden sleepers. Reason : Small sized wooden sleepers are used so that rails exert more pressure on the railway track. Due to which rail does not leave the track

21. Assertion : paper pins are made to have pointed end. Reason : Because pointed pins have very smalll area due to which even for small applied force it exert large pressure on the surface.

19. Assertion : A block of wood is floating in a tank containing water. The apparent weight of the floating block is equal to zero. Reason : Because the entire weight of the block is supported by the buoyant force (the upward thrust) due to water.

15. Assertion : The viscosity of liquid increases rapidly with rise of temperature. Reason : Viscosity of a liquid is the property of the liquid by virtue of which it opposes the relative motion amongst its different layers.

7. Assertion : The velocity increases, when water flowing in broader pipe enter a narrow pipe. Reason : According to equation of continuity, product of area and velocity is constant.

4. Water flows through a frictionless duct with a cross-section varying as shown in fig. Pressure p at points along the axis is represented by

Explanation-(a) When cross-section of duct is decreased, the velocity of water increased and in accordance with Bernoulli’s theorem, the pressure P decreased at that place. (48)

2. A small spherical solid ball is dropped from a great height in a viscous liquid. Its journey in the liquid is best described in the diagram given below by the

(a) Curve A (b) Curve B (c) Curve C (d) Curve D Answer-b (46)

1. A lead shot of 1mm diameter falls through a long column of glycerine. The variation of its velocity v. with distance covered is represented by

Answer-a (48)

65. Consider the following equation of Bernouilli’s theorem.

P + (1/2)ρV2 + ρgh =K(constant) The dimensions of K/P are same as that of which of the following (a) Thrust (b) Pressure (c) Angle …

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 (268)

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 …