A stone is dropped into a quiet lake and waves move in circles at a speed of 4 cm/s. At the instant when the radius of the circular wave is 10 cm, the rate of increase of the enclosed area is:
A stone is dropped into a quiet lake and waves move in circles at a speed of 4 cm/s. At the instant when the radius of the circular wave is 10 cm, the rate of increase of the enclosed area is:
- A. 80π cm²/s
- B. 40π cm²/s
- C. 20π cm²/s
- D. 8π cm²/s
Answer: A) 80π cm²/s
Explanation: dr/dt = 4 cm/s. A = πr². dA/dt = 2πr dr/dt = 2π × 10 × 4 = 80π cm²/s.
0 Answers
Log in to post your own answer or join the discussion.
No comments yet — start the discussion.