Engineering Board Exam Reviewer · Related Rates (Time Rates) · easy
A stone dropped into a still pond sends out a circular ripple whose radius increases at 1.5 ft/s. Find the rate at which the enclosed area is increasing when the radius is 4 ft.
- 12π ft2/s 37.7 ft2/s
- 6π ft2/s
- 24π ft2/s
- 9π ft2/s
Answer
A. 12π ft2/s 37.7 ft2/s
Solution
A=π r2, so dA/dt=2π rdr/dt=2π(4)(1.5)=12π 37.7 ft2/s.
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