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!

Simple Harmonic Motion and displacement

  1. Dec 4, 2009 #1
    1. A 0.69 kg block is hung from and stretches a spring that is attached to the ceiling. A second block is attached to the first one, and the amount that the spring stretches from its unstrained length increases by a factor of 5. What is the mass of the second block?



    2. Force= spring constant*displacement of spring from unstrained length



    3. First off, I'm horrible at algebra so sorry if I make stupid mistakes in this attempt. The force is gravity so that becomes mg (.69kg*9.8 m/s/s).

    mg=kx

    If I pick a spring constant of 10 (does it matter what I pick?) then the equation becomes:

    (.69kg)(9.8m/s/s)=10 x

    Which would give a displacement of .6762 m. Now, when we increase it by a factor of 5, that displacement becomes 3.381 m. Plugging that into a new equations gives:

    m (9.8m/s/s) = 10 (3.381m)

    When I solve for m I get 3.45 kg, which is wrong. Someone tell me what I did wrong?
     
  2. jcsd
  3. Dec 4, 2009 #2
    m is the total mass of the first and second blocks. Try to leave your work in symbols rather than substitute arbitrary numbers; its neater that way.
     
  4. Dec 4, 2009 #3
    So if I leave it in the symbol format I get that (.69kg)(9.8m/s/s)=kx and m(9.8m/s/s)=k(5x). Now what?
     
  5. Dec 5, 2009 #4
    (m1 + m2)g = 5 (kx) = 5 (m1)g
    :. m2 = 4 m1
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Simple Harmonic Motion and displacement
Loading...