### Fluid Mechanics Multiple Choice Questions and Answers

**Ques.** A body is just floating on the surface of a liquid. The density of the body is same as that of the liquid. The body is slightly pushed down. What will happen to the body

(a) It will slowly come back to its earlier position

(b) It will remain submerged, where it is left

(c) It will sink

(d) It will come out violently

**Ques.** If pressure at half the depth of a lake is equal to 2/3 pressure at the bottom of the lake then what is the depth of the lake

(a) 10 m

(b) 20 m

(c) 60 m

(d) 30 m

**Ques.** Two different liquids are flowing in two tubes of equal radius. The ratio of coefficients of viscosity of liquids is 52:49 and the ratio of their densities is 13:1, then the ratio of their critical velocities will be

(a) 4 : 49

(b) 49 : 4

(c) 2 : 7

(d) 7 : 2

**Ques.** The pressure at the bottom of a tank containing a liquid does not depend on

(a) Acceleration due to gravity

(b) Height of the liquid column

(c) Area of the bottom surface

(d) Nature of the liquid

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**Ques.** A hollow sphere of volume *V* is floating on water surface with *half* immersed in it. What should be the minimum volume of water poured inside the sphere so that the sphere now sinks into the water

(a) V/2

(b) V/3

(c) V/4

(d) V

**Ques.** When a large bubble rises from the bottom of a lake to the surface. Its radius doubles. If atmospheric pressure is equal to that of column of water height *H*, then the depth of lake is

(a) H

(b) 2H

(c) 7H

(d) 8H

**Ques.** A capillary tube is attached horizontally to a constant head arrangement. If the radius of the capillary tube is increased by 10% then the rate of flow of liquid will change nearly by

(a) + 10%

(b) + 46%

(c) – 10%

(d) – 40%

**Ques.** Air is blown through a hole on a closed pipe containing liquid. Then the pressure will

(a) Increase on sides

(b) Increase downwards

(c) Increase in all directions

(d) Never increases

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**Ques.** An ice block contains a glass ball when the ice melts within the water containing vessel, the level of water

(a) Rises

(b) Falls

(c) Unchanged

(d) First rises and then falls

**Ques.** A log of wood of mass 120 *Kg* floats in water. The weight that can be put on the raft to make it just sink, should be (density of wood = 600 *Kg/m*^{3})

(a) 80 Kg

(b) 50 Kg

(c) 60 Kg

(d) 30 Kg

**Ques.** Two water pipes of diameters 2 *cm* and 4 *cm* are connected with the main supply line. The velocity of flow of water in the pipe of 2 *cm* diameter is

(a) 4 times that in the other pipe

(b) 1/4 times that in the other pipe

(c) 2 times that in the other pipe

(d) 1/2 times that in the other pipe

**Ques.** A hemispherical bowl just floats without sinking in a liquid of density 1.2 x 10^{3}*kg/m*^{3}. If outer diameter and the density of the bowl are 1 *m* and 2 x 10^{4} *kg*/*m*^{3} respectively, then the inner diameter of the bowl will be

(a) 0.94 m

(b) 0.97 m

(c) 0.98 m

(d) 0.99 m

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**Ques.** A square plate of 0.1 *m* side moves parallel to a second plate with a velocity of 0.1 *m*/*s*, both plates being immersed in water. If the viscous force is 0.002 *N* and the coefficient of viscosity is 0.01 *poise*, distance between the plates in *m* is

(a) 0.1

(b) 0.05

(c) 0.005

(d) 0.0005

**Ques.** A concrete sphere of radius *R* has a cavity of radius *r* which is packed with sawdust. The specific gravities of concrete and sawdust are respectively 2.4 and 0.3 for this sphere to float with its entire volume submerged under water. Ratio of mass of concrete to mass of sawdust will be

(a) 8

(b) 4

(c) 3

(d) Zero

**Ques.** Which of the following is not the characteristic of turbulent flow?

(a) Velocity more than the critical velocity

(b) Velocity less than the critical velocity

(c) Irregular flow

(d) Molecules crossing from one layer to another

**Ques.** A wooden block of volume 1000 cm^{3} is suspended from a spring balance. It weighs 12 N in air. It is suspended in water such that half of the block is below the surface of water. The reading of the spring balance is

(a) 10 N

(b) 9 N

(c) 8 N

(d) 7 N

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**Ques.** The Working of an atomizer depends upon

(a) Bernoulli’s theorem

(b) Boyle’s law

(c) Archimedes principle

(d) Newton’s law of motion

**Ques.** Water falls from a tap, down the streamline

(a) Area decreases

(b) Area increases

(c) Velocity remains same

(d) Area remains same

Fluid Mechanics questions and answers