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Homework Help: Can someone please help

  1. Apr 24, 2008 #1
    1. The problem statement, all variables and given/known data

    A particles position is given by r=42t^2i + 41t^3j + 6k. Calculate the magnitude of its acceleration at time t = 15 seconds

    2. Relevant equations

    3. The attempt at a solution

    to find the acceleration i found the second derivative which i had as 246t + 84. Then i put 15 in as t and got 3774, but according to the answers i should get 3691. What did i do wrong
  2. jcsd
  3. Apr 24, 2008 #2

    Doc Al

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    Staff: Mentor

    You are dealing with vectors. The acceleration is 246tj + 84i, not just 246t + 84.
  4. Apr 28, 2008 #3
    but do i still have to find the second derivative using this? Can you give me a hint on how to do this?
  5. Apr 28, 2008 #4
    ive worked this one out. Thanks for the hint
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