Physics

Fluid Mechanics

637 Questions

Fluid mechanics is a core physics topic that evaluates the principles of liquid pressure, buoyancy, density, and viscosity through complex numerical problems. The questions require calculating the volume of submerged objects, understanding hydraulic jumps, and applying fundamental fluid statics principles. It is a highly scoring subject for candidates preparing for technical and engineering competitive exams.

Liquid pressure and depthBuoyancy and densityVolume expansionHydraulic jump calculationsSurface tension mechanics

Fluid Mechanics Questions

Multiple choice

Directions: A brief passage or a statement is given, and a question is asked, based on the information provided by the passage/statement. The question has four alternatives marked 1 to 4. Critically examine them and choose the best answer.

As per the law of floatation, when a body floats in a liquid, the weight of the body must be equal to the weight of the displaced liquid. Which of the following conditions completes the above law?

  1. The centre of gravity of the body and the centre of gravity of the displaced liquid must be in the same vertical line.

  2. Liquids transmit pressure equally in all directions.

  3. Law of floatation is the principle applied in a hydraulic press.

  4. A steel bar sinks in alcohol, but floats in mercury.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

(4) It is because of the difference in the weights.

Multiple choice

When we pour ice cubes into a jug of water, they float on the water. Why?

  1. Ice is heavier than water.

  2. Ice is solid while water is liquid.

  3. Ice has white colour.

  4. Ice is lighter than water.

  5. All solids float when put in liquid.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Ice is lighter than water. Ice has more space between the molecules than water does. That makes ice float on top of water.

Multiple choice

While scuba diving, a girl notices air bubbles underwater. She observes that the size of a bubble is small when it is deep underwater. But the size increases as it moves upwards. What could be the reason behind the increase in size of the bubble?

  1. It is due to gravity.

  2. Water enters into the bubbles to make them appear larger.

  3. It is due to decrease in pressure applied by water on air bubbles.

  4. Friction

  5. More air enters into the bubbles from top.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

There is decrease in pressure applied by water column on air bubbles as they rise up.

Multiple choice

The density of water is

  1. 1.26 gm/cm3

  2. 1 gm/cm3

  3. 13 .55 gm/cm3

  4. 0.711 gm/cm3

  5. 1.049 gm/cm3
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Yes, it the density of pure water.

Multiple choice

Kerosene floats on water because

  1. kerosene has more density

  2. kerosene has less energy

  3. the density of water is more than kerosene

  4. water has more weight

  5. kerosene has a bad odour
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The density of water is more than kerosene, so it floats on water.

Multiple choice
Directions: The following question consists of certain statements. You have to select the option representing the most logical sequencing of the given statements. A. Density = Mass ÷ Volume. B. Density of iron is very high. C. If density increases mass decreases. D. If density increases volume increases. E. If mass increases volume increases at constant density. F. If mass increases density increases at constant volume.

  1. ABF

  2. AFB

  3. ABE

  4. AFE
Reveal answer Fill a bubble to check yourself
D Correct answer
Multiple choice

Why does an orange sink in pure water but float in salty water?

  1. Because the density of orange is less than density of pure water

  2. Because the density of orange is less than density of salty water

  3. Because the density of orange is more than density of salty water

  4. Because the densities of orange and salt water are the same

  5. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

An orange does not  float in fresh water but since salt water is more dense than fresh water, it has a better chance of floating in the salty water. The greater buoyant force allows the orange to float in the salt water, if salty enough.

Multiple choice

A boat with a man and some stones in it is floating in a pool of water. The man in the boat starts throwing the stones one by one in the water. What will happen to the level of water when he has thrown all stones in the water?

  1. Increase

  2. Decrease

  3. Remain unchanged

  4. First increases and then decreases

  5. Cannot be determined
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

When the boat with the stones was floating in water, a volume of water was being displaced the mass of which was equal to the combined mass of the boat, the man and the stones. When the stones are thrown in water, the boat is displacing a volume of water; the mass of which is equal to that of the combined mass of the man and the boat. Clearly, this volume is less than what was being displaced before. Now, when the stones are thrown in water, they displace a volume of water equal to their own volume. Because of the fact that they sink in the water, the mass of this volume of water must be less than their masses. But when they were floating in the boat, a volume of water had to be displaced the mass of which was equal to that of the stones. Clearly, the volume of water displaced when the stones were in the boat was more than when it is empty. Hence, the water level comes down.

Multiple choice

A toyboat is floating in a tub full of water. It develops a small hole and sinks to the bottom. What will happen to the level of water in the tub?

  1. Increase

  2. Decrease

  3. Remain unchanged

  4. First increases and then decreases

  5. Cannot be determined
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

When the boat was floating in water, it was displacing a volume of water, the mass of which was equal to that of the boat. When the boat sinks, it displaces a volume of water the mass of which must be lesser than that of the boat. Hence, the 2nd volume of water displaced must be less than the 1st. So, the water level would come down.

Multiple choice

It is said that there is a vacuum in a vessel when

  1. air is completely filled in the vessel

  2. air is partially removed from the vessel

  3. air is completely removed from the vessel

  4. water is completely removed from the vessel
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

When air is completely removed from a vessel, it is said that there is vacuum in the vessel.

Multiple choice

A fresh egg sinks in pure water where as it floats in salty water

  1. Due to higher density of salty water

  2. Due to higher density of pure water

  3. Due to fluid matter inside the egg shell

  4. None of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Salt water has higher density than pure water. The egg's density is between the two - it sinks in less dense pure water but floats in denser salt water due to buoyancy.

Multiple choice

Rain drop is always spherical in shape because

  1. liquid tends to possess minimum surface tension area

  2. liquid tends to possess maximum surface tension area

  3. liquid tends to possess zero surface tension area

  4. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The shape of a drop of rain is constrained by the surface tension, which tries to give it the shape for which the surface area is minimum. For a given volume, the spherical shape has the minimum surface area. That is why rain drops acquire spherical shape.

Multiple choice

Which of the following statements is/are false? a. The high air pressure produced by the gas molecules on the walls of baloon causes it to expand and get inflated. b. The pressure exerted by a liquid on the walls of its container increases with the increasing depth. c. The rise of liquid in a dropper is due to the gravitational force.

  1. Only a

  2. Only a and b

  3. Only b

  4. Only b and c

  5. Only c
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

Statement 'c' is a false statement. Thus, it is the correct option. The rise of liquid in a dropper is due to the atmospheric pressure.