F.5 MATHS ..............................
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F.5 MATHS
2010-12-16 6:38 am
回答 (1)
2010-12-16 6:55 am
✔ 最佳答案
(a) dr/dt=d/dt [20(1-e^(-t/2)]
=10e^(-t/2)
Since when r=4, 4=20(1-e^(-t/2)] => e^(-t/2)=4/5
So dr/dt |r=4=10(4/5)=8 m/s
(b) dV/dt=4πr^2(dr/dt)
when r=4, dr/dt=8 m/s by the result of (a). So dV/dt=(4π)(4^2)(8)=512π m^3/s
(c) After a long time r-> 20 m. So V=4πr^3/3+2π=32006π/3 m^3.
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原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20101215000051KK01462