1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Velocity Dependent Forces

  1. Nov 6, 2012 #1
    1. The problem statement, all variables and given/known data
    A 1000kg boat is traveling at 25 m/s when its engine is shut off. The magnitude of the frictional force f between the boat and the water is proportional to the speed v of the boat: f=70v, where v is in meters per second and f is in newtons. Find the time required for the boat to slow to 12.5 m/s.

    2. Relevant equations

    3. The attempt at a solution
    70v = (1000 kg) * a
    a(t) = 70v(t) / (1000 kg)

    However, after this point I don't know what to do. I can't use the formula v2 = vo2 + 2a(Δx), because I don't know Δx. I don't know how I would find the anti-derivative of a(t), since a(t) is defined in terms of v(t). What am I missing?
  2. jcsd
  3. Nov 7, 2012 #2
    Does this look right?

    Attached Files:

  4. Nov 7, 2012 #3
    It probably is, but I don't understand it. We haven't gotten that far in ap calculus yet, so I'll ask my teacher about how that works tomorrow. Thanks for the help!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook