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Force Elevator Problem!

  1. Oct 13, 2010 #1
    1. The problem statement, all variables and given/known data
    Your mass is 65 kg. You stand on a bathroom scale in an elevator on Earth.

    (a) What force would the scale exert when the elevator moves up at a constant speed?

    (b) What force would the scale exert when it slows at 2.1 m/s2 while moving upward?

    (c) What force would the scale exert when it speeds up at 2.1 m/s2 wile moving downward?

    (d) What force would the scale exert when it moves downward at a constant speed?

    (e) What force would the scale exert when it slows to a stop at a constant magnitude of acceleration?

    2. Relevant equations
    f=ma
    fg=mg
    fnet=mAnet
    Ff=μῦFn


    3. The attempt at a solution
    I honestly have no idea what to do with all these Y forces going everywhere..Can someone walk me through the process of solving this problem?

    THANK YOU IN ADVANCE FOR ANY HELP!!
     
  2. jcsd
  3. Oct 13, 2010 #2

    PhanthomJay

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    Draw free body diagrams. There are 2 forces acting on the person, the person's weight, acting down, and the normal (scale) force acting up. Use Newton's laws F_net = ma when accelerating. At constant speeed or at rest, F_net =0 (no acceleration, per newton 1). Please show an attempt .
     
  4. Oct 13, 2010 #3
    I found (a), (c), and (d), but I can't find (b). Here is my attempt at solving it:

    mAnet = -Fn + Fg
    mAnet - Fg = -Fn
    65(-2.1) - 65(9.81) = -Fn
    774.15 = Fn

    Help?
     
  5. Oct 13, 2010 #4
    I also don't understand how to find (e)..
     
  6. Oct 13, 2010 #5
    Okay after working on this, I've solved it. Thanks anyways!
     
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