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Homework Help: Relative Velocity

  1. Jun 30, 2008 #1
    1. The problem statement, all variables and given/known data
    John equation of motion is Rj(t)=(t^2+3t)i + tj. David's equation of motion is Rd(t)=5ti+t^3j. At t=1 find David's velocity with respect to john.

    2. Relevant equations

    3. The attempt at a solution I know if you plug in the one that will give you the position they are both at when t=1. Where do I go from there to find their velocity?
  2. jcsd
  3. Jun 30, 2008 #2
    It's a dead end if you plug in t=1 in the first place. Instead, you should differentiate the positions with respect to time to find the velocities. Hint:
    [tex]\frac{d}{dt} (x^n) = nx^{n-1}[/tex]
  4. Jun 30, 2008 #3
    Ok, that makes a lot more sense! I believe that's going to help me out! Thanks. I was just totally looking past that.
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