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!

An Elevator Problem

  1. Oct 7, 2004 #1
    Here's the problem:
    A person stands on a bathroom scale in a motionless elevator. When the elevator begins to move, the scale briefly reads only 0.75 of the person's regular weight. Calculate the acceleration of the elevator, and find the direction of acceleration.

    I honestly don't know how to get this problem started. I'm assuming gravity has a part to play in this, and based on the "0.75", i'm guessing the elevator is going down. Can anyone offer tips to get this problem rolling?

    Thanks in advance
     
  2. jcsd
  3. Oct 7, 2004 #2

    Pyrrhus

    User Avatar
    Homework Helper

    Do a force analysis using

    Newton's 2nd Law

    [tex] \sum_{i=1}^{n} \vec{F}_{i} = m \vec{a} [/tex]
     
  4. Oct 7, 2004 #3
    I'm a little rusty on my physics (i'm actually helping a friend here, its not my problem). Could you please explain a little more what you mean?

    One more thing, calculus shouldn't be required for this problem, it just covers Newton's Laws (as you mentioned). I think i'm overlooking something obvious here :grumpy:

    Thanks for taking a look, i really appreciate it!
     
    Last edited: Oct 7, 2004
  5. Oct 7, 2004 #4

    Pyrrhus

    User Avatar
    Homework Helper

    The person will have a movement while in the elevator in the Y-axis. or an acceleration of [tex] \vec{a} = +/- a_{y}j [/tex], depending where its heading. Which you have to find out. Test it on both directions and see which equation is the proper one.
     
    Last edited: Oct 7, 2004
  6. Oct 7, 2004 #5
    Ok so based on that (and the info i was given)... it looks like the elevator is heading downward, with the person's acceleration increasing in the [tex]- a_{y}j[/tex] direction. Am I on the right track?
     
    Last edited: Oct 7, 2004
  7. Oct 7, 2004 #6

    Gokul43201

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Right track, so far ! But it wouldn't be right to say "acceleration increasing in the..". There is no indication that the acceleration is changing.

    But yes, the acceleration is downwards.
     
  8. Oct 7, 2004 #7

    Gokul43201

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Did you draw a free body diagram ? This is the first thing to do. What are the forces on the man ? Relate the net force to the acceleration (see post #2) and you're home !
     
  9. Oct 12, 2004 #8
    Thanks for the help, we got it finally!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: An Elevator Problem
  1. Elevator Problem (Replies: 1)

  2. Elevator problem (Replies: 3)

  3. Elevator problem (Replies: 1)

  4. Elevator problem (Replies: 7)

  5. Elevator Problem (Replies: 5)

Loading...