1. Not finding help here? Sign up for a free 30min 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!

Block attached to spring - calculate how far it will move

  1. Jun 16, 2013 #1
    1. The problem statement, all variables and given/known data
    A spring with spring constant 200 N/m is suspended vertically with its upper end fixed to the ceiling and its lower end at position y = 0. A block of weight 20 N is attached to the lower end, held still for a moment, and then released. How far will the block move before coming momentarily to a stop?


    2. Relevant equations
    mg = -kx
    mg = 0.5kx^2


    3. The attempt at a solution
    I tried using the first equation and got x = 0.1m as my ans. which was wrong. I then tried using the second equation instead and still got an incorrect answer. Where am I going wrong? The ans. is 0.2 m.

    Thanks in advance!
     
  2. jcsd
  3. Jun 16, 2013 #2

    lewando

    User Avatar
    Gold Member

    You need to look at this problem from an energy conservation standpoint.
     
  4. Jun 16, 2013 #3
    The block comes to a stop when its speed is zero. Your approach is invalid because the speed of the block is not necessarily zero when the net force acting on the block is zero.
     
  5. Jun 16, 2013 #4
    Hmm ok would it be something like this? mgh = 0.5kx^2 and the x and the h are the same? Cuz then solving for h I get (2mg)/k and when I subbed in the number I got 0.2. Is this the right way of doing this problem?
     
  6. Jun 16, 2013 #5

    lewando

    User Avatar
    Gold Member

    Looks like a good way to get the answer!
     
  7. Jun 16, 2013 #6
    Your answer is correct; however, it is important you understand why the approach is valid. Do you?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted