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!

What am I doing wrong in my calculations

  1. Jan 29, 2013 #1
    What is the distance the upper spring is extended from its unstretched length?
    Now, three masses m1 = 3.3 kg, m2 = 9.9 kg and m3 = 6.6 kg hang from three identical springs in a motionless elevator. The springs all have the same spring constant of 229.57N/m

    Now the elevator is moving downward with a velocity of v = -2.3 m/s but accelerating upward with an acceleration of a = 4.8 m/s2. (Note: an upward acceleration when the elevator is moving down means the elevator is slowing down.)

    What is the distance the upper spring is extended from its unstretched length?
    cm


    I did

    (3.3(9.8+4.8))/229.57=0.20987 m =20.987 cm
     
  2. jcsd
  3. Jan 29, 2013 #2

    SammyS

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    That looks good to me.

    Is there a problem regarding significant digits?
     
  4. Jan 29, 2013 #3
    Hi I am not sure my answer is supposed to be in cm but I am sure I have done it right puzzling indeed
     
  5. Jan 29, 2013 #4

    rl.bhat

    User Avatar
    Homework Helper

    In your problem you have mensioned three springs and three masses. Whether the springs are connected with each other? If yes, who?
     
  6. Jan 29, 2013 #5
    springs are connected is m1 at top is connected to m2 in middle which is connected to m3 in the bottom
     
  7. Jan 29, 2013 #6

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    So, the spring at the top is supporting, directly or indirectly, all three masses? Won't that increase the tension in it?
     
  8. Jan 29, 2013 #7
    this is the pic
     

    Attached Files:

  9. Jan 29, 2013 #8

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    Right, so what is the tension in the top spring? If you're not sure, start with the free body diagram of the bottom mass and work up.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: What am I doing wrong in my calculations
  1. What Am I Doing Wrong? (Replies: 2)

  2. What am I doing wrong? (Replies: 1)

Loading...