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Homework Help: Kinetic and Potential Energy?

  1. Oct 9, 2005 #1
    Kinetic and Potential Energy!?!

    This problem is totally confusing me..can someone please explain it...:confused:

    A 3.0 kg object subject to a restoring force F is undergoing simple harmonic motion with a small amplitude. The potential energy U of the object as a function of distance x from its equilibrium is shown. This particular object has a total energy E: of 0.4 J.

    (a) What is the object's potential energy when its displacement is +4 cm from its equilibrium position?
    For this problem, I used 4 cm as my displacement, but when I used it in the formula, I ended up getting an answer that is greater than the total energy, so I know it must be wrong. Am I using the wrong displacement?

    (b) What is the farthest the object moves along the x-axis in the positive direction? Explain.
    I really don't understand how to solve for the distand in the x-axis without having the acceleration or time. Is there a formula that I've overlooked or am I just making this problem more complicated than it is?

    (c) Determine the object's kinetic energy when its displacement is -7 cm.
    For this part, the kinetic energy equation is KE= 1/2mv^2. How do I solve for the velocity without time or acceleration?

    (d) What is the object's speed at x= 0?
    Again, I would need the answers from (c) to solve for the speed.
  2. jcsd
  3. Oct 9, 2005 #2


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    Is there an image?
  4. Oct 9, 2005 #3


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    For part 9 (a). Mind your units. The units for Joules is: 1 Joule = 1 kgm^2/s^2.
    If you are using cm, you will not be getting Joules, but rather "centi-Joules" :P

    For part (b). The energy of a oscillator can be expressed as the sum of it's potential (1/2kx^2) and kinetic (1/2mv^2). At max displacement, it has zero kinetic energy.
  5. Oct 9, 2005 #4
    There is a graph of the distance and potential energy. When the problem states that it is 4cm from its equilibrium position, is it referring to the x or y component?
  6. Oct 9, 2005 #5


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    I believe we are talking about a 1 dimensional oscillator, and that dimension is the x?
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