JEE Main Physics: Fluid Mechanics Practice Questions

Correct answer: C — Shear deformation

The Modulus of Rigidity, or Shear Modulus (G), measures the material's resistance to deformation by shear stress, which results in a change in shape (angular deformation).

Correct answer: A — It will be doubled.

Since drag force is proportional to the density of the fluid, doubling the density effectively doubles the drag force required to balance gravity, thus doubling the terminal velocity.

Correct answer: C — It is doubled

Since drag force is directly proportional to velocity (F ∝ v), doubling the velocity will double the drag force.

Correct answer: C — The velocity and the radius

Stoke's Law states that the drag force is proportional to the product of viscosity (η), radius (r), and velocity (v), i.e., F ∝ ηr v.

Correct answer: A — change in shape

The modulus of rigidity measures the material's resistance to elastic deformation, specifically changes in shape (stretching or shearing) when a force is applied.

Correct answer: A — The dynamic viscosity of the fluid

Viscosity (η) is the primary factor determining the fluid's resistance to flow, and thus it is the most critical property for calculating drag according to Stoke's Law.

Correct answer: D — Newton per meter (N/m)

Moduli (like Young's Modulus and Bulk Modulus) are measures of stress (Force/Area) over strain, so their unit is the Pascal (Pa), which is equivalent to N/m². However, when discussing the modulus itself, the base units derived from stress and strain relations are consistent with N/m² (or Pa). Since the options relate to standard physical quantities, the relation involving stress/strain yields Pa. (Note: Often, Modulus unit is Pa or N/m², which is equivalent to N/m when dealing with linear elastic deformation).

Correct answer: B — Cohesion and adhesion

Capillary rise is caused by the balance between the upward force due to adhesion (liquid sticking to the tube walls) and the downward force due to gravity, modified by surface tension forces. This is governed by the balance of cohesive and adhesive forces.

Correct answer: A — Increasing as the speed increases.

As the speed of the object increases, the drag force increases, causing the terminal velocity to increase until the balance condition is met.

Correct answer: A — 90°

For a flat surface in equilibrium with a horizontal surface, the angle between the surface and the fluid surface (and thus the angle of contact) is 90 degrees if we consider the angle relative to the normal, or 0 degrees if we consider the angle relative to the surface itself depending on the precise definition used; in this context, it implies a perpendicular contact if the setup is perfectly flat against a horizontal surface.

Correct answer: B — It has infinite resistance to volume change

Incompressibility means the material strongly resists changes in volume under pressure, corresponding to an infinite Bulk Modulus (K → ∞).

Correct answer: C — The object's mass and the drag force.

Terminal velocity is determined by the balance between gravitational force and the drag force. Therefore, the object's mass and the drag force are the critical factors.

Correct answer: B — It is doubled

Since F ∝ r, doubling the radius while keeping other factors constant will double the resulting drag force.

Correct answer: D — Bulk Modulus

The Bulk Modulus (K) specifically measures the resistance of a substance to uniform compression, which directly relates to its resistance to volume change.

Correct answer: B — Analyzing the pressure distribution across a submerged surface.

The angle of contact is fundamentally used to analyze how the pressure exerted by the fluid is distributed and balanced across the solid boundary (the submerged surface).