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Homework Help: Test of power on a swinging mass striking an object

  1. Sep 22, 2008 #1
    1. Hello, I need to devise myself a practical coursework and i have chosen to find out how several variables effect the power of a swinging mass striking an object.

    I will use a motor to swing an arm of 30cm with a 1kg mass attached to the end with a time period of 1 second. The arm will be swung around parallel to the floor (not like a windmill) and i will vary to following to see the effects it has on strength:

    Firstly i will do the test varying the length of the arm
    Secondly i will do the test varying the weight of the mass
    Thirdly i will do the test verying the time period

    2. Relevant equations
    I am not sure of what equations to use but have found on wikipedia several equations on power such as
    power = work/time
    power = force x displacement
    power(t) = Torque(t) x Angular Velocity(t)

    which of these if any do i use and does anyone have any suggestion or hints and tips on how to make this practical experiment go well?

  2. jcsd
  3. Sep 23, 2008 #2
    In uniform motion all the power used by the motor is to overcome the friction forces. I believe, what you want to quantify is the amount of energy, which is carried by the moving mass and then is transferred into the collision. This energy is just the total kinetic energy:

    [tex]E = \frac{mv^2}{2} = \frac{m(\omega L)^2}{2} = \frac{m}{2} \left(\frac{2\pi L}{T}\right)^2\\
    = 2\pi^2 \frac{mL^2}{T^2}[/tex]

    Here m is your mass, L is the arm length and T is the period. I'm not sure what are you going to measure, but probably the idea is to obtain something like: "The dependence of the amount of destruction on energy of collision". You will somehow measure the destruction and the energy can be calculated by the formula given above.

    Good luck with the experiment!
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