A spherical ball of salt is dissolving i...

A spherical ball of salt is dissolving in water in such a manner that the rate of decrease of the volume at any instant is propotional to the surface. Prove that the radius is decreasing at a constant rate.
Hint for solution : Take volume V and curve surface are S of spherical ball. Calculate by taking `(dV)/(dt)alpha S`.

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The correct Answer is:

`(dr)/(dt)=k`

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