A stone is dropped into a quite lake and waves move in circles at the rate of 5 cm/sec. At the instant when radius of the circular wave is 8 cm, how fast is the enclosed area increasing?
contexto.140
Let cm be the radius of the circular wave at time
Rate of increase of radius of circular wave = 5 cm/sec
is positive and = 5 cm/sec
Let be the enclosed area of the circular wave.
Rate of change of area = =
= =
Putting = 8 cm (given),
= cm2/sec
Since is positive, therefore area of circular wave is increasing at the rate of cm2/sec.
