Two drops of same radius are falling through air with steady velocity of v cm s⁻¹. If the two drops coalesce, the terminal velocity x₁/3 v. What is the value of x.
Physics · Properties of solid and fluid
JEE Mains Practice

Question

Two drops of same radius are falling through air with steady velocity of v cm s⁻¹. If the two drops coalesce, the terminal velocity x₁/3 v. What is the value of x.

G1 Physics · Accepted Answer

Step 1: Use surface-energy/pressure relations: ΔP = 2T/R for a liquid drop or 4T/R for a soap bubble, capillary rise h = 2T cosθ/(ρgr), and surface energy = TΔA. Step 2: Apply force or energy balance to the stated radii and surface areas. Applying these relations to the given data gives 4. Final answer: 4.