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Thread: particle moving

  1. #1
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    particle moving

    a particle starts from rest and moves in a horizontal line with speed v given by dv/dt = 80-v
    (i)find the time taken for the particle to increase its speed from 20 m/s to 40 m/s
    (ii)using the fact that the integral of (v/80-v) dv = 80-v-80ln(80-v)+c find how far the particle travels in going from rest to a speed 60 m/s
    (iii) determine the limiting speed of the particle i.e v->v1 as t-> infinity

    I was able to do part i using definite integrals and the answer I got was .405

    I am stuck on (ii) and (iii)
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  2. #2
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    Re: particle moving

    ii) $\dfrac{ds}{dv} = \dfrac{\dfrac{ds}{dt}}{\dfrac{dv}{dt}}=\dfrac{v}{ \dfrac{dv}{dt}}=\dfrac{v}{80-v}$
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  3. #3
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    Re: particle moving

    thanks I will try it again now
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