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Solução_Calculo_Stewart_6e

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F.<br />

214 ¤ CHAPTER 4 APPLICATIONS OF DIFFERENTIATION<br />

TX.10<br />

77. (a) First note that 90 mi/h =90× 5280<br />

3600 ft/s = 132 ft/s. Then a(t) =4ft/s2 ⇒ v(t) =4t + C,butv(0) = 0 ⇒<br />

C =0.Now4t =132when t = 132<br />

4<br />

=33s, so it takes 33 s to reach 132 ft/s. Therefore, taking s(0) = 0,wehave<br />

s(t) =2t 2 , 0 ≤ t ≤ 33. Sos(33) = 2178 ft. 15 minutes = 15(60) = 900 s, so for 33

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