1. Not finding help here? Sign up for a free 30min 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!

Variation on momentum q

  1. Aug 9, 2011 #1
    If a 1kg object is moving at 3m/s in a positive direction, and a 12N force is applied in the negative direction, what is the velocity immediately after 2s?

    I'm fairly sure this will be a variation of relevent momentum equations, and/or mixed with kinematics, yet I'm not seeing the correct application. I lean towards answers c or b.

    Obviously mo will be conserved.


    conservation of mo: m1Vi= (m1+m2)vf t=v/a



    a. 12m/s
    b. 6 m/s
    c. 3 m/s
    d. 0 m/s

    Please explain.
     
  2. jcsd
  3. Aug 9, 2011 #2
    I'm afraid you can't use conservation of momentum here - that only applies in the absence of an external force (in the relevant direction), and here the problem says there's a 12 N force. Do you know any other way you might go about solving this?
     
  4. Aug 9, 2011 #3
    What you need is the impulse formula. Whenever time is involved for a force it's almost always Impulse.

    Definition: The Impulse (I) imparted onto a body is the change in it's momentum. Impulse is a vector quantity.

    Derivation: F = ma

    F = m (v-u)/t
    F = mv - mu /t
    Ft = mv -mu



    Unit is obviously Newton seconds.
     
  5. Aug 9, 2011 #4
    Yes, I do believe this is on the right track, so thanks, but

    I believe I'm remiss in something. What is u?

    I'm recalling something like.......Ft=mvf-mvi (change in p)
     
    Last edited: Aug 9, 2011
  6. Aug 10, 2011 #5
    u = initial velocity
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Variation on momentum q
  1. Physics Q - momentum (Replies: 8)

Loading...