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Unformatted text preview: to (aqt73) – Section 3.8 – isaacson – (55826) 1 This printout should have 5 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. 001 10.0 points A rock is thrown into a still pond and causes a circular ripple. If the radius of the ripple is increasing at a rate of 6 ft/sec, at what speed is the area of the ripple increasing when its radius is 2 feet? 1. speed = 24 sq. ft/sec 2. speed = 23 sq. ft/sec 3. speed = 23 π sq. ft/sec 4. speed = 25 sq. ft/sec 5. speed = 21 π sq. ft/sec 6. speed = 21 sq. ft/sec 7. speed = 22 π sq. ft/sec 8. speed = 24 π sq. ft/sec correct Explanation: The area, A , of a circle having radius r is given by A = πr 2 . Differentiating implicitly with respect to t we thus see that dA dt = 2 πr dr dt . When r = 2 , dr dt = 6 , therefore, the speed at which the area of the ripple is increasing is given by speed = 24 π sq. ft/sec . 002 10.0 points A street light is on top of a 10 foot pole....
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This note was uploaded on 06/14/2011 for the course MATH 305G taught by Professor Cathy during the Spring '11 term at University of Texas.
 Spring '11
 Cathy

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