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!

Compression of Spring

  1. May 20, 2010 #1
    1. The problem statement, all variables and given/known data
    A 2kg block is dropped from a height of 40 cm onto a spring of force constant k=1960 N/m. Find the maximum distance the spring is compressed.

    (The answer must be 10 cm)

    3. The attempt at a solution

    Well, I know that if a spring is stretched "y", it will be compressed "y". The problem is that I can't find out how long will the spring stretch once it is dropped from that height. Therefore I tried to use the formula

    [tex]F = ky[/tex]

    Where [tex]F= mg = 2 \times 9.81[/tex] and k =1960 N/m which is 196000 N/cm

    [tex]2 \times 9.81 = (196000) k[/tex]

    [tex]y= \frac{2 \times 9.81}{196000}[/tex]

    But this gives me the wrong answer. Why is that?? :confused:

    By the way, I know that the tension is [tex]T= 2 \pi \sqrt{\frac{m}{k}} = 2 \pi \sqrt{\frac{2}{196000}}= 0.02 N[/tex].
  2. jcsd
  3. May 21, 2010 #2


    User Avatar
    Homework Helper

    It is best to consider energy for this problem, graviational pe = potential pe of spring

    Also that T is period time and not the tension.
  4. May 21, 2010 #3
    I tried that, it doesn't seem to work:

    [tex]mgh= \frac{1}{2} k x^2[/tex]

    2 (9.81) 40 = 1/2 (196000) x2

    x=0.089 cm

    Because the correct answer should be 10 cm! Is there anything wrong with my calculations?

    Yep, my mistake. :blushing:
  5. May 21, 2010 #4


    User Avatar
    Homework Helper

    Not sure, the only way to get 10cm exact is if the mass was dropped from 50cm.

    Normally, the energy method should work.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Compression of Spring
  1. Spring max compression (Replies: 25)

  2. Compression of spring (Replies: 2)

  3. Compressed springs (Replies: 11)