Q. 64.1( 26 Votes )
The radius of a circle is increasing at the rate of 0.7 cm/s. What is the rate of increase of its circumference?
Answer :
We know that circumference of a circle (C) is C = 2πr
Then, Rate of change of circumference with respect to time (t) is given by,
……………….. by chain rule
It is given that
Then, 
Therefore, the rate of increase of its circumference is 1.4π cm/s.
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PREVIOUSA stone is dropped into a quiet lake and waves move in circles at the speed of 5 cm/s. At the instant when the radius of the circular wave is 8 cm, how fast is the enclosed area increasing?NEXTThe length x of a rectangle is decreasing at the rate of 5 cm/minute and the width y is increasing at the rate of 4 cm/minute. When x = 8cm and y = 6cm, find the rates of change of (a) the perimeter, and (b) the area of the rectangle.
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