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: Drag Force

  1. Jul 11, 2009 #1
    1. The problem statement, all variables and given/known data
    A baseball is thrown straight up. The drag force is proportional to v^{2}.
    In terms of g, what is the y-component of the ball's acceleration when its speed is half its terminal speed and it is moving up? In terms of g, what is the y-component of the ball's acceleration when its speed is half its terminal speed and it is moving back down?

    2. Relevant equations

    v terminal = [tex]\sqrt{mg/D}[/tex]

    3. The attempt at a solution
    I honestly have no idea how to attempt this problem
     
  2. jcsd
  3. Jul 11, 2009 #2
    The drag force is of the form:
    [tex]F_d = -kv^2[/tex]

    Or to use your notation:
    [tex]F_d = -Dv^2[/tex]

    The terminal velocity is achieved when the ball starts falling at a constant velocity. At that point, the following holds true:
    [tex]kv^2=mg[/tex]
     
  4. Jul 11, 2009 #3

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    Hi clarineterr! :wink:

    Start "acceleration = dv/dt = … " :smile:
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook