Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: PE problem

  1. Oct 20, 2005 #1
    I just need to make sure I understand how to do this and that I am doing everything correctly. Could someone check my work please?


    You place the spring vertically with one end on the floor. You then drop a 1.70 kg book onto it from a height of 0.70 m above the top of the spring. Find the maximum distance the spring will be compressed.
    So
    k_1 + U_1 + W_{other} = k_2 + U_2
    I have that

    k_1=0, U_1= mgy_1, W_o=0, k_2=0, U_2=1/2kx^2

    So the issue is that I have to the potential energy to the start of the spring plus the distance the spring compresses.

    To solve this I need to adjust the equations to look like

    mg(y+x)=1/2kx^2

    This works out to a homogenous quadradic that looks like

    1/2kx^2-mgx-mgy=0

    Plugining in values and solving gets me

    0.142 meters.

    TIA

    T
     
  2. jcsd
  3. Oct 20, 2005 #2

    Diane_

    User Avatar
    Homework Helper

    You didn't include the spring constant, so I can't check your arithmetic, but your reasoning looks faultless to me. Good job. :)
     
  4. Oct 21, 2005 #3
    oops...sorry about that.

    It should be 1400N/m...and thanks :smile:
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook