1. Limited time only! Sign up for a free 30min personal 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!

Weight on an elevator question torturing me

  1. Oct 9, 2009 #1
    A 88.0 kg person stands on a scale in an elevator. What is the apparent weight in each of the following situations?
    (a) when the elevator is accelerating upward with an acceleration of 1.40 m/s2

    (b) when the elevator is moving upward at a constant speed

    (c) when the elevator is accelerating downward with an acceleration of 1.70 m/s2

    in my text it talks about apparent weight on an elevator and gives the equation:

    Force Normal = mg + ma

    then it doesn't say a darn thing afterwords. no example or anything.

    my attempted solutions:

    a) a= 9.8 + 1.4 = 11.2 m/s^2

    F = (88kg x 9.8m/s^2)+(88kg x 11.2m/s^2)= 1795.2 N

    b) the elevator isn't moving so the apparent weight would be the same as the normal weight
    w = mg = 88 x 9.8 = 862.4N

    c) a = 9.8 - 1.7 = 8.1m/s^2

    F = (88 x 9.8)+(88 x 8.1)= 1575.2n

    i know a and c can't make sense because they are worked the same way and c is greater b. c should be less than b


    am i using the formula wrong?
     
  2. jcsd
  3. Oct 9, 2009 #2

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    No, a= 1.4. g is 9.8

    This should be either 88kg x 9.8 m/s^2+ 88kg*1.4m/s^2 or 88kg(9.2+ 1.4)= 88kg(11.2m/s)

    Yes, that is correct.

    Again you are using g twice. a= -1.7 so either 88*9.8- 88*1.7 or 88(9.8- 1.7).

    "a" is the acceleration of the elevator as given. You do not add 9.8 to that to get a.
     
  4. Oct 9, 2009 #3
    thank you my friend.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Weight on an elevator question torturing me
  1. Weight In An Elevator (Replies: 6)

  2. Elevator Weight (Replies: 10)

  3. Weight in an elevator (Replies: 1)

Loading...