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Homework Help: Curvilinear Motion: Rectangular Components

  1. Jan 27, 2013 #1
    1. The problem statement, all variables and given/known data

    What is the magnitude of the velocity at t=4.00s?

    I would like to see if my approach and answer is correct.

    2. Relevant equations

    Position: r = {-30cos([itex]\frac{\pi}{10}[/itex]t) i + 30sin([itex]\frac{\pi}{10}[/itex]t) j - (7t) k} ft

    3. The attempt at a solution

    I took the first derivative to get the velocity and my equation came out to be:

    r' = {3[itex]\pi[/itex]sin([itex]\frac{\pi}{10}[/itex]t) i + 3[itex]\pi[/itex]cos([itex]\frac{\pi}{10}[/itex]t) j - (7) k} [itex]\frac{ft}{s}[/itex]

    And after plugging in t=4, my velocity vector equation was: [(8.96)i + (2.91)j - (7)k] [itex]\frac{ft}{s}[/itex]

    Then my velocity magnitude was: 11.74 [itex]\frac{ft}{s}[/itex]
  2. jcsd
  3. Jan 27, 2013 #2


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    Homework Helper

    It is OK, but the result can not be accurate to four significant digits.

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