tailieunhanh - Calculus: An Integrated Approach to Functions and their Rates of Change, Preliminary Edition Part 86

Calculus: An Integrated Approach to Functions and their Rates of Change, Preliminary Edition Part 86. A major complaint of professors teaching calculus is that students don't have the appropriate background to work through the calculus course successfully. This text is targeted directly at this underprepared audience. This is a single-variable (2-semester) calculus text that incorporates a conceptual re-introduction to key precalculus ideas throughout the exposition as appropriate. This is the ideal resource for those schools dealing with poorly prepared students or for schools introducing a slower paced, integrated precalculus/calculus course | Finding Mass When Density Varies 831 Observe the following. We did not simply integrate p h . There was a 28 in the integrand as well. Let s parse the integral. We are summing p h 28 dh from h 0 to h 3 corresponding to density in mg vol. area of slice thickness of slice or density in mg vol. volume of a slice. The limits of integration while not explicit in the summation notation of the Riemann sum are implicitly there. As n hi 0 and hn_1 3. The limits of integration are always determined by the endpoints of the interval being chopped up. EXAMPLE SOLUTION When a meteorite crashes into the earth debris is scattered nearby. Suppose that the density of debris is modeled by p r 1-2 kilograms per square meter where r is the number of meters from the center of the meteorite s impact. What is the mass of the debris that lies within 10 meters of the center of impact In order to flnd mass we need to multiply density by area. Density is not constant so we will need to use a slicing approach to break the problem down into regions where the density is approximately constant. KEY NOTION Just as in Example we must slice in a way that keeps the density approximately constant within each slice. In this case density depends on r the distance from the center of impact. Accordingly we subdivide the r-interval 0 10 into n equal subintervals each of length 10 Ar m we label r0 r1 r2 . rn as shown. The slices that result from this are concentric circular rings. Unlike in the rock sample example in this situation the area of the slices varies. I----1-----1----L- 0 r1 r2 r3 II r0 J----1----1 rn-1 10 II rn Figure The mass in the ith ring the approximate density in the ring the area of the ith ring . What is the area of the ith ring Intuitive Approach Think of the ith ring as made of yarn. If the ring is thin enough its inner and outer circumferences are approximately equal. To approximate the area clip the yarn and unbend it laying it out as a long narrow rectangle. The

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