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: Find x dot as function of t

  1. Sep 28, 2008 #1
    1. The problem statement, all variables and given/known data

    find velocity x dot, as function of time t, for particle mass m starts x=0, t=0
    subject to force where Fo and c are constants.

    Fx = Fo + ct

    2. Relevant equations

    answer is

    x dot =Fo/m t + c/2m t^2

    3. The attempt at a solution

    obviously it is just an integration.
    but how does the "m" get in there.

    i know this is a simple question, but the solution eludes me

    i have stuff like

    F=mv dot = m r dotdot
    x dotdot = dv/dt = F/m = a = constant

    what is Fx - is the the force component in direction x , or is it a vector , ?
    what is Fo - a constant, vector?

    how do you add in a t

    how about

    Fx dt = Fo dt + ct dt

    Fo = ma = m v dot

    x dot = int Fo dt + int ct dt

    = int dt + 1/2 c t^2

    ... and im lost
  2. jcsd
  3. Sep 28, 2008 #2


    User Avatar
    Homework Helper
    Gold Member

    [tex]F_x[/tex] is the x-component of the total force on the particle and so

    [tex]F_x=ma_x=m \ddot{x}=m \frac{d^2x}{dt^2}[/tex]

    Is that enough to get you started?
  4. Sep 28, 2008 #3
    i think i got it .....

    i did f=ma

    a = f/m = x dot dot

    so ....

    x dot = ∫ Fo/m +∫ ct/m

    is that the right method .....
  5. Sep 28, 2008 #4


    User Avatar
    Homework Helper
    Gold Member

    Looks fine so far (I'm assuming you're integrating over dt). What do you get?

    edit- make sure you include a constant of integration.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook