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Homework Help: Friction/Kinematics problem

  1. Sep 5, 2004 #1
    A 1000 kg boat is travelling at 90 km/h when its engine is shut off. The magnitude of the frictional force, fk, between boat and water is proportional to the speed, v, of the boat: fk = 70v, where v is in meters per second and fk is in newtons. Find the time required for the boat to slow to 45 hm/h.

    Now, I have absolutely no clue as to what to do. I've tried alot of different things and they have all led absolutely nowhere. I do know however that the a = 0.07v. Thats about all i can say for sure :cry: . Could someone nudge me in the right direction?
  2. jcsd
  3. Sep 5, 2004 #2


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    Does this help?

    [tex]m\frac{dv}{dt} = -70v[/tex]
  4. Sep 5, 2004 #3
    Never mind, i figured it out.
  5. Sep 5, 2004 #4
    Yes it did tide, but you were about 10 seconds to late :P.
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