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Simple Harmonic Motion question

  1. Apr 14, 2008 #1
    [SOLVED] Simple Harmonic Motion question

    1. The problem statement, all variables and given/known data
    A 0.27 kg block oscillates back and forth along a straight line on a frictionless horizontal surface. Its displacement from the origin is given by the following equation.
    x = (15 cm)cos[(5 rad/s)t + /2 rad)]
    (a) What is the oscillation frequency? .796 Hz
    (b) What is the maximum speed acquired by the block? 75cm/s
    At what value of x does this occur? 0cm
    (c) What is the magnitude of the maximum acceleration of the block? 375cm/s^2
    At what values of x does this occur? (Type your answers in any order. If there is only one answer, type 'none' in the second box.) -15cm 15cm
    d) What force, applied to the block, results in the given oscillation?
    2. Relevant equations
    x(t)=Xm Cos(wt+phi)
    F=-kx

    3. The attempt at a solution
    I solved parts athrough c but I was not sure what to do for part d.
    I had already solved for k in part a so I substituted the values for k and Xm into the F=-kx equation
    F=-6.75(N/m) .15m=1.0125N
    the form webassign wants the answer in is (_____ N/cm)x
     
  2. jcsd
  3. Apr 14, 2008 #2
    # Hi
    # I think there may be a mistake in the question. The dimensionality of the force is N not N/cm.
     
  4. Apr 14, 2008 #3
    notice that the answer is in the form of (-----N/cm)x. the question is asking for the force F=-kx so would the answer be k with units of N/cm instead of N/m?
     
  5. Apr 14, 2008 #4
    # Oh, yes. I did not see x there. Then, I think your reasoning seems plausible. You should write -k in units of N/cm there.
     
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