Multiple Choice Questions (MCQs) on fluid mechanics class 11 : Physics advocate/advguruji

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Q1. Hairs of shaving brush cling together when it is removed from water due to-

(a) force of attraction between hair

(b) surface tension

(c) viscosity of water

(d) characteristic property of hair

Q2. Coatings used on raincoat are waterproof because they -

(a) increases angle of contact

(b) decreases angle of contact

(c) does not alters angle of contact

(d) forms a smooth surface

Q3. A body measures 5 N in air and 2 N when put in water. The buoyant force is-

(a) 7 N

(b) 9 N

(c) 3 N

(d) None of these

Q4. A hole is made at the bottom of the tank filled with water (density = 1000 kg/m³). If the total pressure at the bottom of the tank is three atmospheres (1 atmosphere = 10⁵ N/m²), then the velocity of efflux is nearest to-

(a) 20 m/s

(b) 10√2 m/s

(c) 20√2 m/s

(d) √500 m/s

Q5. When the temperature is increased the angle of contact of a liquid?

(a) increases

(b) decreases

(c) remains the same

(d) first increases and then decreases

Q6. The surface tension of a soap solution is 20 mN/m. To blow a bubble of radius 1 cm, the work done is

(a) 4π μJ

(b) 8π μJ

(c) 12π μJ

(d) 16π μJ

Q7. The excess pressure due to surface tension in a spherical liquid drop of radius r is directly proportional to-

(a) r

(b) r²

(c) 1/r

(d) 1/r²

Q8. A raft of mass M = 600 kg floats in calm water with 7 cm submerged. When a man stands on the raft, 8.4 cm are submerged, the man's mass is -

(a) 30 kg

(b) 60 kg

(c) 90 kg

(d) 120 kg

Q9. An ideal fluid flows through two pipes of circular cross-section with diameters 2.5 cm and 3.75 cm connected one after another. The ratio of the velocities in the two pipes is -

(a) 9:4

(b) 3:2

(c) √3:√2

(d) √2:√3

Q10. If a water drop is kept between two glass plates, then its shape is -

Q11. Two small drops of mercury each of radius r form a single large drop. The ratio of surface energy before and after this change is -

Q12. Two rain drops of same radius r falling with terminal velocity v, merge and form a bigger drop of radius R. The terminal velocity of the bigger drop is -

Q13. Air stream flows horizontally past an aeroplane wing of surface area 4 m². The speed of air over the top surface is 60 m/s and under the bottom surface is 40 m/s. The force of lift on the wing is (density of air = 1 kg/m³) -

(a) 800 N

(b) 1000 N

(c) 4000 N

(d) 3200 N

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ANSWERS

A1. (b)

A2. (a)

A3. (c)       A4. (a)

A5. (b)

A6. (d)       A7. (c)

A8. (d)

A9. (a)      A10. (c)

A11. (a)

A12. (b)    A13. (c)

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