Physics-DPP-4-Fluid Mechanics

PHYSICS Topic: FLUID MECHANICS Date: 1. A U-tube in which the cross-sectional area of the limb on the left is one quarter. The limb on the right contains mercury çædensity = 13.6 g cm ö÷. The level of mercury in the narrow limb is at a distance of 36 cm from the upper end of the tube. What will be the rise in the level of mercury in the right limb, if the left limb is filled to the top with water ? (a) 1.2 cm (b) 2.11 cm (c) 0.53 cm (d) 0.8 cm 2. Two cylinders of same cross-section and length L but made of two materials of densities d1 and d2 are cemented together to a form a L cylinder of length 2 L. The combination floats in a liquid of density d with a length 2 above the surface of the liquid. If d1< d2 then : (a) d < 3 d (b) d > d (c) d > d (d) d > 3 d 1 4 2 1 4 1 1 4 3. A tank is filled up to a height 2H with a liquid and is placed on a platform of height H from the ground. The distance x from the ground where a small hole is punched to get the maximum range R is : (a) H (b) 1.25 H (c) 1.5 H (d) 2 H 4. A flow of liquid through two capillary tubes connected in series. Their length are l and 2l and redius r and 2r respectively. Then the pressure difference across the first and second tubes are in the ratio : (a) 1/8 (b) 4 (c) 2 (d) 8/1 5. Speed of a ball of 2 cm radius in a viscous liquid is 20 cm/s. Then the speed of 1 cm radius of ball in the same liquid is : (a) 80 cm/s (b) 40 cm/s (c) 10 cm/s (d) 5 cm/s 6. A drum of radius R full of liquid of density d is rotated about an axis touching its surface at  rad/s. The increase in pressure at the centre of the drum will be : (a) ω2 R2d 2 2 (b) ωRd 2 2 (c) ω2 Rd 2 (d) ω2R2d 2 7. The force required to separate two glass plates of area 10–2 m2 with a film of water 0.05 mm thick between them is : (surface tension of water is = 70  10–3 N/m) : (a) 28 N (b) 14 N (c) 50 N (d) 38 N 8. Two glass plates are separated by water. If surface tension of water is 75 dyne/cm and area of each plate wetted by water is 8 cm2 and the distance between the plates is 0.12 mm, then the force applied to separate the two plates is : (a) 102 dyne (b) 104 dyne (c) 105 dyne (d) 106 dyne 9. A given shaped glass tube having uniform cross-section is filled with water and is mounted on a rotatable shaft as shown in figure. If the tube is rotated with a constant angular velocity , then : (a) Water levels in both sections A and B go up (b) Water level in section A goes up and that in B comes down (c) Water level in section A comes down and that in B is goes up (d) Water levels remain same in both sections 10. By sucking through a straw, a student can reduce the pressure in his lungs to 750 mm of Hg (density = 13.6 g/cm3). Using the straw, he can drink water from a glass upto a maximum depth of : (a) 10 cm (b) 75 cm (c) 13.6 cm (d) 1.36 cm PHYSICS Topic: FLUID MECHANICS Date: Answer Key 1. (c) 2. (a) 3. (c) 4. (d) 5. (d) 6. (d) 7. (a) 8. (c) 9. (a) 10. (c)

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