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

A child has two beakers. In the first beaker, he poured some drinking water and in the other, he poured some seawater. He tests the solutions with a tester and compass needle. In which case will the compass needle deflect more?

  1. The beaker with drinking water will show more deflection.

  2. Both the beakers will show the same deflection.

  3. The beaker with seawater will show more deflection.

  4. The beaker with seawater will show no deflection.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The beaker with seawater will show more deflection as seawater being salty is a better conductor. As more current flows through the seawater, the deflection shown by the needle will be more.

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. More air enters into the bubbles from top

  2. Due to friction

  3. Due to gravity

  4. Due to decrease in pressure applied by water on air bubbles

  5. Due to dissolved oxygen more at the surface
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

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

Multiple choice

The sludge from the aeration tank of the activated sludge process (ASP) has solids content (by weight) of 2%. This sludge is put in a sludge thickener, where sludge volume is reduced to half. Assume that the amount of solids in the supernatant from the thickener is negligible, the specific gravity of sludge solids is 2.2 and the density of water is 1000 kg/m3.

What is the density of the sludge removed from the aeration tank?

  1. 990 kg/m3

  2. 1000 kg/m3

  3. 1011 kg/m3

  4. 1022 kg/m3
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

 

Multiple choice

The sludge from the aeration tank of the activated sludge process (ASP) has solids content (by weight) of 2%. This sludge is put in a sludge thickener, where sludge volume is reduced to half. Assume that the amount of solids in the supernatant from the thickener is negligible, the specific gravity of sludge solids is 2.2 and the density of water is 1000 kg/m3.

What is the solids content (by weight) of the thickened sludge?

  1. 3.96%

  2. 4.00%

  3. 4.04%

  4. 4.10%
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

 

Multiple choice

A solids sphere (diameter 6 mm) is rising through oil (mass density 900 kg/m3, dynamic viscosity 0.7 kg/ms) at a constant velocity of 1 cm/s. What is the specific weight of the material from which the sphere is made? (Take g = 9.81 m/s2)

  1. 4.3 kN/m3

  2. 5.3 kN/m3

  3. 8.7 kN/m3

  4. 12.3 kN/m3
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

For a sphere moving at constant velocity, the drag force (Stokes' Law) plus buoyancy equals the weight. Solving for the specific weight of the sphere material gives the result.