Coefficient of viscosity by terminal velocity — NEET & JEE Questions

Question 1 · difficulty L1 · recall

Viscosity measures a fluid's resistance to

• A. electric current only
• B. magnetic flux
• C. relative motion between neighbouring layers
• D. nuclear decay

Question 2 · difficulty L1 · understanding

Stokes' law for drag on a small sphere moving slowly through a viscous fluid is

• A. F=πηr²v²
• B. F=6πρrv
• C. F=ηv/(6πr)
• D. F=6πηrv

Question 3 · difficulty L2 · understanding

Terminal velocity is reached when

• A. net force on the falling sphere becomes zero
• B. gravity vanishes
• C. viscosity becomes zero
• D. the sphere stops moving

Question 4 · difficulty L2 · application

For a sphere of radius r in the Stokes regime, terminal velocity varies approximately as

• A. r
• B. r²
• C. 1/r
• D. 1/r²

Question 5 · difficulty L2 · understanding

When a small sphere falls through a viscous liquid and reaches terminal velocity,

• A. the net force on it is zero
• B. its acceleration is maximum
• C. viscous drag is zero
• D. its weight is zero

Question 6 · difficulty L3 · application

If fluid viscosity doubles with all else fixed, terminal velocity

• A. doubles
• B. quadruples
• C. halves
• D. stays unchanged

Question 7 · difficulty L3 · application

A sphere denser than the liquid reaches terminal speed because increasing speed causes

• A. weight to decrease to zero
• B. buoyant force to become infinite
• C. mass to vanish
• D. viscous drag to increase until forces balance

Question 8 · difficulty L3 · application

According to the Stokes-law terminal-velocity relation, terminal speed of a small sphere is proportional to

• A. the square of its radius
• B. its radius only
• C. the inverse square of its radius
• D. the cube of its radius

Question 9 · difficulty L3 · application

Two small spheres of the same material fall through the same viscous liquid. If one sphere has twice the radius of the other, its terminal speed is approximately

• A. twice as large
• B. four times as large
• C. eight times as large
• D. half as large

Question 10 · difficulty L4 · analysis

Why should the sphere's terminal speed be measured away from the liquid surface and container bottom?

• A. To reduce entry transients and boundary effects
• B. To make gravity larger
• C. To eliminate buoyancy
• D. To change sphere radius