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Homework Help: Acceleration due to gravity on planet

  1. Nov 17, 2007 #1
    On your first trip to Planet X you happen to take along a 150 g mass, a 40-cm-long spring, a meter stick, and a stopwatch. You're curious about the acceleration due to gravity on Planet X, where ordinary tasks seem easier than on earth, but you can't find this information in your Visitor's Guide. One night you suspend the spring from the ceiling in your room and hang the mass from it. You find that the mass stretches the spring by 30.4 cm. You then pull the mass down 10.3 cm and release it. With the stopwatch you find that 9.00 oscillations take 18.1 s.

    I tried g on planet X = 0.304m((2pi(9/18.1))^2)/0.103) = 28.8

    But, it's not right. I'm not sure what I'm doing wrong
  2. jcsd
  3. Nov 17, 2007 #2
    How did you come to that equation?

    I think you need a differential equation mass-spring system and the basic equation: F=kx.
    Last edited: Nov 17, 2007
  4. Nov 17, 2007 #3


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    You then pull the mass down 10.3 cm and release it
    Period of oscillation does not depend upon how much you pull it down before you release it.
  5. Nov 18, 2007 #4
    different problem

    okay, I have a question about a different problem

    A 150 g mass attached to a horizontal spring oscillates at a frequency of 1.60 Hz. At t =0, the mass is at x= 5.40 cm and has v_x =- 17.0 cm/s. Determine: the amplitude and the phase constant.

    I have already figured out the period and angular frequency to be 0.625 s and 10.053 rad/s, respectively.

    I'm confused about how you find amplitude though? I'm not sure which equations to apply. note that vx is not equal to v max, so that's why I'm confused.
  6. Nov 18, 2007 #5


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    Oscillation of a horizontal spring is given by x = Asin(wt + phi) and velocity of the mass is given by dx/dt = Awcos(wt + phi). Substitue the values and find the amplitude and the phase.
    Last edited: Nov 18, 2007
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