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Homework Help: Measure the acceleration due to gravity on a distant planet

  1. Feb 17, 2009 #1
    1. The problem statement, all variables and given/known data

    To measure the acceleration due to gravity on a distant planet, an astronut hangs a 0.055 kg ball from the end of a wire. the wire has a length of 0.95 n and a linear density of 1.2*10
    ^-14 kg/m. using electronic equipment, the astronaut measures the time for a transverse pulse to travel the length of the wire and obtains a value of 0.016 s. the mass of the wire is negligible compared to the mass of the ball.
    a) draw a nice picture
    b) calculate the velocity of the pulse
    c)determine the acceleration due to gravity

    2. Relevant equations

    f = v/2L
    v = (Mg/mu)^sq. root

    3. The attempt at a solution

    m = 0.055 kg
    L = 0.95 m
    mu = 1.2*10^-4 kg/m
    T = 0.016 s

    b)f = 1/0.016s = 62.5 hz
    v = 2fL = 2*62.5 hz*0.95 m = 118.75 m/s

    c)g = (v^2*mu)/M = {(118.75 m/s)^2*1.2*10^-4 kg/m}/0.055 kg = 30.77 m/s^2

    i got both of them wrong. where did i screw up?
  2. jcsd
  3. Feb 17, 2009 #2

    Doc Al

    User Avatar

    Staff: Mentor

    This is a pulse, not a standing wave. The speed of the pulse is simply distance/time.
  4. Feb 17, 2009 #3
    a) i have attached the picture to check it.

    so for b) v = L/t = 0.95 m/ 0.016 s = 59.38 ms^-1

    and c) g = {(59.38 m/s)^2 * 1.2*10^-4 kg/m}/ 0.055 kg = 7.69 m?s^2.


    Attached Files:

    • 1.JPG
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  5. Feb 17, 2009 #4

    Doc Al

    User Avatar

    Staff: Mentor

    Looks good to me.
  6. Feb 17, 2009 #5
    appreciate it man
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