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Homework Help: Find the time required for the boat to slow to 45 km/hr

  1. Dec 6, 2004 #1
    hey

    A 1000 kg boat is travelling at 90km/h when its engine is shut off. The magnitude of the frictional force between boat and water is proportional to the speed v of the boat: force of kinetic fricition=70v, where v is in meters per second and the force is in newtons. Find the time required for the boat to slow to 45 km/hr
     
  2. jcsd
  3. Dec 6, 2004 #2

    dextercioby

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    Homework Helper

    I'm a theorist,so i'll let u plug the numbers:
    The Newton's law states:[itex] m\frac{dv}{dt}=-\alpha v [/itex],where alpha is that 70 in your problem:
    Integrate the ODE wrt to proper limits:
    Final result:[itex] t=(\frac{1000}{70}\ln 2) s [/itex]

    Good luck!!
     
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