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!

Vectors, Check my work.

  1. Feb 6, 2009 #1
    1. The problem statement, all variables and given/known data

    A particle of mass 2.0 kg has position given by the vector r = (t^4 -3t^3) i + (t^3 - 9t) j + (2t -6) k
    (where i, j, and k are the unit direction vectors and r is given in meters and t in seconds. At what time in seconds is the particle located at the origin?

    For this I get t = 3(seconds).

    It's the second part I want you to check.

    1. what is the magnitude of the particle's velocity (in m/s) when the particle is at the origin?

    2. For the particle in question 1, what is the x/y/z-component of the net force (in Newtons) acting on it when it is at the origin? Do not write Newtons as part of your answer.

    2. Relevant equations

    V = Dr / Dt
    F= Ma

    3. The attempt at a solution

    1. Derive each component individually. Got:

    (4t^3-9t^2)i, (3t^2 - 9)j, (2)k
    Plug in 3 to get. 27 + 18 + 2 = Sqrt 47 = 6.86 m/s while at origin.

    2. Derived each component again to get the acceleration eq.
    I got (12t^2 - 18t)i, (6t)j, and (0)k

    Then did F = MA for each component.

    2.0(12(3)^2 - 18(3)) = 108 for x component.
    2.0(6(3)) = 36 for the y component.
    2.0(0) = 0 for the z component.

    Did I do this correctly?

    Thanks for helping :D.
     
  2. jcsd
  3. Feb 6, 2009 #2

    gabbagabbahey

    User Avatar
    Homework Helper
    Gold Member

    Hi Kaln0s, welcome to PF! :smile:

    Don't you have to square each component before summing them up and taking the square root?:wink:

    [tex]||\vec{v}||=\sqrt{v_x^2+v_y^2+v_z^2}[/tex]


    Looks good to me:approve:
     
  4. Feb 6, 2009 #3
    Oh god I feel dumb as hell lol. I've been doing Calculus and physics non-stop for the past day -_-.

    27^2 + 18^2 + 2^2 = 1057 sqrt = 32.5 m/s
    :rofl:

    Thank you very much. :biggrin:
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Vectors, Check my work.
  1. Please check my work (Replies: 2)

Loading...