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Homework Help: Mechinical vibration - simple

  1. Feb 22, 2009 #1
    so u = -cos(t) + sqrt(3)sin(t)

    so the Wo = 1, and R =2, but how do i find delta?

    tan(del) = sqrt(3)/-1, but the answer has it as

    u = 2cos(t-2pi/3)

    i can't get the 2pi/3 no matter what i do...

    thanks
     
  2. jcsd
  3. Feb 22, 2009 #2
    If you follow the posting guidelines I think it will be easier for someone to answer you. The question doesn't seem to be very clear.
     
  4. Feb 22, 2009 #3
    acutally, i found my mistake!
     
  5. Feb 22, 2009 #4
    um one more question, what should be the unit for metric?

    should i do it in kg, m, seconds, always?

    thanks
     
  6. Feb 22, 2009 #5
    yeah always use SI units
     
  7. Feb 22, 2009 #6
    haha

    ok, ONE LAST QUESTION (of this thread)..

    how do i know when it's "weight" or "mass"? is it in the wordings of the problem?

    thanks
     
  8. Feb 22, 2009 #7
    Weight is a vector, a force. You can see that the dimensions of a force would be kg m/s^2 or Newtons. Mass is a scalar quantity and will be measured, if in SI units, in kg only.

    F=MA

    Weight = mg

    where m is mass and g is the acceleration due to gravity
     
  9. Feb 22, 2009 #8

    thanks!
     
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