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Homework Help: How to find scale weight?

  1. Oct 22, 2011 #1
    1. The problem statement, all variables and given/known data
    A weighs 600 N on an elevator when it is stationary. Each elevator accelerates according to the specified arrow that is drawn next to it. In all cases where the elevator is moving, it is moving downward.
    Find net force, if the elevator is accelerating 2.0 m/s/s upward, even though the elevator is moving downward. Use g = 9.8 m/s/s

    2. Relevant equations
    w = mg
    F = ma

    3. The attempt at a solution
    Well this is what i did: F = ma
    Fn - mg = ma
    Fn = ma + mg
    Fn = 61.2(2) + 61.2(9.8)
    Fn = 722.4 N
    Is that right?
  2. jcsd
  3. Oct 22, 2011 #2
    That question seems contradictory. It's accelerating upward, even though it's moving downward? That isn't what Newton's Laws state.
  4. Oct 22, 2011 #3
    well the elevator is moving downward, and if the accleration is upward, doesnt that mean that the elevator is slowing down?
  5. Oct 22, 2011 #4
    My apologies, you're right. I haven't worked dynamics in a while. Regardless, your work looks good.
  6. Oct 22, 2011 #5
    So our scale weight is increasing as we're going down? Shouldnt it be decreasing? Because my teacher said, that the formula should be Fn = ma + -mg
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