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: Motion Formulas

  1. Sep 2, 2006 #1
    hey,
    I’ve been wondering for quite sometime now that if I am given values for displacement, time, and final velocity if it were able to calculate the acceleration and the initial velocity? I have been trying to rearrange the formulas:

    [tex]v = u + at[/tex]

    [tex]v^2 = u^2 + 2as[/tex]

    [tex]s = ut + .5at^2[/tex]

    but have been unsuccessful. I would like to know if it were possible to calculate the unknowns using the values given, thanks,
    Pavadrin
     
  2. jcsd
  3. Sep 2, 2006 #2

    Päällikkö

    User Avatar
    Homework Helper

    From the first equation:
    [tex]a = \frac{v-u}{t}[/tex]

    Substitute to the third.
     
  4. Sep 2, 2006 #3
    That still wouldn't be helpful seeing the initial velocity is unknown, what would be helpful is another equation:

    [tex]s = t \frac{v+u}{2}[/tex]

    And transpose to give

    [tex] u = \frac{2s}{t} - v[/tex]

    There is another way to calculate a as well using the 3rd formula, make ut = vt and - the [tex].5at^2[/tex]. Which will give you the right answer, you can test it by substituing fake values in.
     
  5. Sep 2, 2006 #4

    Päällikkö

    User Avatar
    Homework Helper

    Sure it would.
    Making the substitution:

    [tex]s = ut + \frac{1}{2}(v-u)t[/tex]

    [tex]u = 2 \frac{s}{t} - v[/tex]
     
  6. Sep 2, 2006 #5
    Ah, of course.
     
  7. Sep 2, 2006 #6
    okay thanks for the help everyone :smile:
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook