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!

Impulse-Momentum Theorem Q.

  1. Jun 30, 2005 #1
    I have this problem that says a 3 kg object has a velocity of 7.00m/s j (vertical, right?). Then a total of 12.0Ni (horizontal) acts on it for 5 seconds. What is the objects final velocity.

    I know that the equation is Ft=mvf-mvi

    I could just plug everything in, but what's bothering me is the fat that the mass has an vertical velocity and the force is acting on it horizontally. Am I reading this wrong or is this the case?

    If so, how do I go avout finding what I need to plug in.

    My work:

    Ft=mvf-mvi
    (12N)(5s)=(5)(vf)-(5)(7)... then solve for vf, but that seems too easy.
     
  2. jcsd
  3. Jun 30, 2005 #2
    The object is moving in the vertical direction with that velocity, yes and then the force acts on it for 5 seconds. So yeah, that is the case.

    You still use [itex]\vec{F}t = m(\vec{v_{f}} - \vec{v_{i}})[/tex] and solve for [itex]\vec{v_{f}}[/itex], but writing the force and inital velocity in terms of vectors and not just their magnitudes.
     
    Last edited: Jun 30, 2005
  4. Jun 30, 2005 #3

    OlderDan

    User Avatar
    Science Advisor
    Homework Helper

    The motion in the x direction is independent of the motion in the y direction. Since there is no y-directed force, the y-velocity will be unchanged. In you last equation, you should only have x-directed quantities. You substituted the wrong number for mass, and you have the wrong initial velocity.

    After you get the final x-velocity, you need to add it to the y-velocity by vector addition.

    OOPs- scooped again :smile:
     
  5. Jun 30, 2005 #4
    ohhh i didn't mean to put in 5 as the mass :)
    so i have to find the initial velocity first? it's not just 7 huh.....
    then find the final V and doo Vector addition,

    ok thank you all very much!!!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Impulse-Momentum Theorem Q.
Loading...