Q. What is the radius of the biggest aluminium coin of thickness $t$ and density$\rho$, which will still be able to float on the water surface of surface tension$S$?
A) $\frac{4\ S}{3\rho\ g\ t}$
B) $\frac{3\ S}{4\rho\ g\ t}$
C) $\frac{2\ S}{\rho\ g\ t}$
D) $\frac{S}{\rho\ g\ t}$
Explanation
(c) Let $R$ be the radius of the biggest aluminium coin which will be supported on the surface of water due to surface tension. Then, $mg = S \times 2\pi R$
or $\pi R^{2}t\rho g = S \times 2\pi R$
Or $R = 2S/\rho gt$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.