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Homework Help: Kinematic question

  1. Apr 28, 2010 #1
    1. The problem statement, all variables and given/known data
    A body of mass m is thrown upward with intial velocity u, in a medium which exerts a resistance force of mkv. Express, in term of g, k and u, the time taken for the body to reach its maximum height

    2. Relevant equations

    3. The attempt at a solution

    a = -g - kv
    dv/dt = -g - kv
    -dv/(g+kv) = dt
    t = -1/k ln|g+kv| +c
    when t = 0, v=u
    c = 1/k ln|g+ku|
    t = -1/k ln|g+kv| + 1/k ln|g+ku|
    At maximum height, v = 0
    Thus t = -1/k ln|g| + 1/k ln|g+ku|
    Is my working correct?
  2. jcsd
  3. Apr 28, 2010 #2
    looking quickly i think so....... cant see any problems
  4. Apr 28, 2010 #3
    wait... if taking gravity as negative the resistive force would be + first equation?....
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