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: Trajectory help

  1. Feb 15, 2009 #1
    A particle's trajectory is described by x=((1/2)t^3 - 2t^2) and y=((1/2)t^2-2t) , where t is in s.

    What is the particle's speed at t= 4.5 s?
    What is the particle's direction of motion, measured as an angle from the x-axis, at t=4.5 s?

    I keep geting the wrong answers >:0 , how do I go about solving this?
  2. jcsd
  3. Feb 15, 2009 #2


    User Avatar
    Gold Member

    How did you try solving this? Show us so we can explain where you went wrong.
  4. Feb 15, 2009 #3
    Take the derivative of both.

    Then solve for t = 4.5s, us these vector components to find the angle.
    Last edited: Feb 15, 2009
  5. Feb 15, 2009 #4
    Alright, so i dont know why I wasnt getting the right answer before(i was taking the derivatives), but I took the derivatives for x and y, then used the sqrt(x^2+y^2) to get part one. Then y=cos^-1(x/v) for part two.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook