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MHT CET 2026 (20 Apr, Shift 1) · Surface Energy & Work Done

Surface Energy & Work Done question from MHT CET 2026 (20 Apr, Shift 1)

Q2MHT CET 2026 · 20 APR · SHIFT 1Medium

Surface Energy & Work Done

If $450$ erg of work is done in blowing a soap bubble of radius ' $r$ ', the additional work required to be done to blow it to a radius equal to $3r$ is

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Answer: (c)

A bubble has two surfaces: $W = T\times 2\times 4\pi r^2 = 8\pi r^2 T$ , so $W \propto r^2$ .
At radius $3r$ : $W' = 9 \times 450 = 4050$ erg.
Additional work $= 4050 - 450 = 3600$ erg.
So the answer is (c) $3600$ erg.

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