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Homework Help: Experimentally Determine the Mass!

  1. May 1, 2012 #1
    My lab topic for tomorrow is to develop two ideas to experimentally determine an unknown mass. We are given a few known masses (I'm not sure how massive), and any materials that are found in most community college physics labs(e.g. force probes(with the little hooks on the ends), force probes(with the little magnets), springs, motion sensors, etc.).

    The prelab assignment is to find two methods, and I have three, but fear the 3 hour lab period tomorrow might be dull if I only use these three.

    Here are my methods in order of what I suppose are the most accurate:

    1) Using a force probe(with the little hook on the end) and a known mass, determine the μk from dragging it across a surface. Use that determined coefficient drag the unknown mass across that same surface and get the mass.

    2) Pick a spring capable of holding the unknown mass without warping, and use a force probe and a ruler to determine its spring coefficient. Use that coefficient to weigh the unknown mass.

    3) Use a couple force carts(with magnets) and a motion sensor, determine the impulse (area under the force-time curve)and divide the impulse by the Δv. I have already done this method and it is finicky so I will try to avoid it.

    That's all I can think of so far; if you have an idea and are not sure If we have covered it in class mention it anyways, and I'll read up on it in my physics book tonight.
  2. jcsd
  3. May 1, 2012 #2
    I found out another method:

    Using a two carts with velcro to mimic an inelastic collision, determine the mass of the carts using a method above. Using a motion sensor track the empty cart(m1)colliding with the other stationary cart with the unknown mass(m2), and assuming all momentum is conserved use: m1v1= (m1+m2)vf
  4. May 1, 2012 #3


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    Staff: Mentor

    You may want to modify slightly your method 1; Does the coefficient of friction depend only upon the "table" surface, or is it a property of both the table surface and the surface of the object at their areas of mutual contact? Hint: Think about two different objects being dragged across the same surface (say, a block of ice and a block of ice wrapped in sandpaper of the same mass).

    Other possible areas to ponder include levers (balances), harmonic motions, centripetal forces.
  5. May 2, 2012 #4
    Right, I would assume that both the unknown mass and known masses are similar enough metals to have the same coefficient.
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