1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Apparent weight on an elevator. Magnitude of its acceleration?

  1. Oct 2, 2008 #1
    1. The problem statement, all variables and given/known data
    You are standing on a bathroom scale inside an elevator. Your weight is 160 lb, but the reading of the scale is 123 lb.
    (a) What is the magnitude and direction of the acceleration of the elevator?
    ??? m/s2
    (b) Can you tell whether the elevator is speeding up or slowing down?
    do not know
    slowing down
    speeding up


    2. Relevant equations
    weight=mg
    ma=ma


    3. The attempt at a solution

    160lbs = 75.574kg

    123lbs: 55.792kg

    g= 9.8ms

    obviously, the elevator is accelerating downwards, reducing his apparent weight.

    his weight when on the ground is 740.625N.

    So, 740.625=55.792a
    a=13.27475. The question is asking for magnitude, but there is no x component so sqrt(a^2) would still be 13.27475

    Obviously, this isnt correct. Can someone point me in the right direction?
     
  2. jcsd
  3. Oct 2, 2008 #2

    LowlyPion

    User Avatar
    Homework Helper

    If it was slowing down while going up it could read the same. All you know is acceleration is less down on the scales.
     
  4. Oct 2, 2008 #3
    Ahh, you're right. That makes sense - I didnt think of that.


    I tried using -13.27, and subtracting 9.8. What am I missing with the calculation?

    Thank you for the tip!
     
  5. Oct 2, 2008 #4

    LowlyPion

    User Avatar
    Homework Helper

    You can divide by like equations.

    9.8/160 = x/123

    I know the units are silly but they cancel as long as your acceleration is to be in m/s2

    The difference then with 9.8 must be the acceleration in the same direction as g.
     
  6. Oct 3, 2008 #5
    Thank you so very much!!

    I was able to figure it out after a bit of tweaking.

    This place is the best =D. I've tried to go through answering peoples questions- but I find that I either cannot answer them well enough, or someone has already beat me to it. I'll try to give back as much as I can
     
  7. Oct 3, 2008 #6

    LowlyPion

    User Avatar
    Homework Helper

    You're welcome. Glad that it helped. All contributions welcome.

    Cheers.
     
  8. Oct 3, 2008 #7
    Maybe I'm wrong, but I think it should be 546.762=75.574a so a=7.234.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Apparent weight on an elevator. Magnitude of its acceleration?
Loading...