JEE Main 2022 · 26 Jul · Shift 1 · Physics Q45

← JEE Main 2022 · 26 Jul · Shift 1

PhysicsSingle correct+4 / -1Question 45 of 90

A water drop of radius 1 cm is broken into 729 equal droplets. If surface tension of water is 75 dyne/cm, then the gain in surface energy upto first decimal place will be :

(Given $\pi=3.14$ )

8.5\times10^{-4}

8.2\times10^{-4}

7.5\times10^{-4}

5.3\times10^{-4}

Answer and worked solution

Official answer: C

Droplet radius $\frac19$ cm; extra area $4\pi(729r^2-R^2)=4\pi\times8$ cm².

Energy $75\times32\pi\times10^{-7}\approx7.5\times10^{-4}$ J.

(C)

Topics:Surface tension

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JEE Main 2022 · 26 Jul · Shift 1, Physics question 45