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

Best of Luck

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

(a) force of attraction between hair

(b) surface tension

(d) characteristic property of hair

Q2. Coatings used on raincoat are waterproof because they -

(a) increases angle of contact

(b) decreases 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

(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

(d) √500 m/s

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

(a) increases

(b) decreases

(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

(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

(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

(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

(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

(d) 3200 N

---------------------------------------------

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)

Feel free to comment your thoughts :-)

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