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Homework Help: Newton's Second Law Problem

  1. Oct 29, 2008 #1
    1. The problem statement, all variables and given/known data
    A 60.0 kg person stands on a scale in an elevator. (solve in Newtons)
    What does it read when the elevator is accelerating upward at 3.5 m/s2?
    What does it read when the elevator is accelerating downward at 3.5 m/s2?

    2. Relevant equations
    Fnet = ma

    3. The attempt at a solution
    First I set up the equation
    Fnet = ma
    (588.6 + X) = 60 x 3.5
    588.6 + X = 210
    X = -378.6
    So then I plugged in X
    588.6 + -378.6 = 210

    I know that this is wrong but I'm not sure what I need to fix/change
  2. jcsd
  3. Oct 29, 2008 #2
    I would look at it a lot more simply: You know that gravity applies an acceleration to masses (9.8 ms-2).

    If the elelavtor is not moving, that's all the acceleration a body feels, however when the evelator is accelerating upwards, a body feels this acceleration as well as the acceleration due to gravity.

    I would simply sum up the gravitational acceleration and acceleration due to the elevator and then apply F = ma.
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