Kinetic and Potential Energy?

  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. Pyrrhus

    Pyrrhus 2,204
    Homework Helper

    Is there an image?
  4. mezarashi

    mezarashi 658
    Homework Helper

    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. 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. mezarashi

    mezarashi 658
    Homework Helper

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