A stone dropped into a pond of still water sends out concentric circular waves from the point of disturbance of water at the rate of 4cm/sec. Find the rate of change of disturbed area at the instant when the radius of wave ring is 15cm.
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Solution
Let the radius of the ring be r
So, according to question,
drdt=4cm/sec
let area be A=πr2,
So, Rate of change of disturbed area = dAdt=2πr.drdt