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Homework Help: Hello, I need some clarification with my lab report

  1. Nov 4, 2014 #1
    1. The problem statement, all variables and given/known data
    Would it be possible for someone to look over the parts of my lab report. If there is anything that I did not mention in the abstract, please inform me. I wasn't sure how I should end the paragraph. My teacher wants us to write our opinion on the success of the experiment (supported by results) but I am still confused about some of the questions. Specifically, I need help with calculating the percent of energy lost in the system.

    2. Relevant equations:
    - In attachment

    3. The attempt at a solution

    In a homework problem, I understood that kinetic energy is transferred to potential energy with rotational momentum conserved and that from that height can be derived. I don't know how to find that kinetic energy for the pendulum. I know that to find initial kinetic energy, I add the kinetic energy of both objects (1/2 mv^2) and to find final kinetic energy, I would use the final velocity of the mass (1/2(m1 + m2) * Vfinal = Kfinal. However, I don't believe that the same formula is used to find the potential energy for the experiment.

    Thank you

    Attached Files:

  2. jcsd
  3. Nov 4, 2014 #2


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    Homework Helper

    For the pendulum you assume that the kinetic energy at the bottom (just after it caught the ball and the ball came to rest in the cradle) is converted to the potential energy at the top of the swing.
  4. Nov 4, 2014 #3
    Thank you for replying.
    I understand that I can set the kinetic energy at the bottom to the potential energy at the swing but I would need to use
    K(initial) = 1/2 (mass of ball + Mass of pendulum) * v^2(initial)
    K(final) = (mass of ball + Mass of pendulum) * 9.81 * height ?

    How can I use the height that was calculated with the initial speed of the ball. I have the velocity of the ball as it is released, but then I have the kinetic energy. Then I set that equal to the kinetic energy of the pendulum and the ball.
    1/2(mass of ball) * velocity of ball^2 = 1/2(mass of ball + mass of pendulum) * velocity of both objects^2
    I found find the velocity of both the objects and then set it equal to the potential energy to find the height?
  5. Nov 4, 2014 #4


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    The Ki would not include the mass of the pendulum since it is initilally stationary isn't it?
    Can't you calculate the height with the angle and length of the pendulum?
    The percentage lost would then be ΔK/Ki x 100
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