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Homework Help: Derivative of position question

  1. Sep 24, 2015 #1
    1. The problem statement, all variables and given/known data

    The position of a dragonfly that is flying parallel to the ground is given as a function of time by r⃗ =[2.90m+(0.0900m/s2)t^2]i^− (0.0150m/s3)t^3j^ .

    At what value of t does the velocity vector of the insect make an angle of 30.0 ∘ clockwise from the x-axis?
    2. Relevant equations

    3. The attempt at a solution
    What I did so far: Well I'm pretty sure the first step is to take the derivative of the position vector. I did that and got (0.18t)i^2-(0.045t^2)j^2.

    I tried to use tan30=0.18t/0.048t^2 and solve for t

    I get t=69.28 but I'm not sure if that is 100% correct
  2. jcsd
  3. Sep 24, 2015 #2


    User Avatar
    Gold Member

    Check this part of the question:

    What can you defer from this?

    I believe your evaluation of "t" has some mistakes.
  4. Sep 24, 2015 #3
    never mind I got it

    was trying to do it too fast and ended up making a careless mistake

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