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!

Homework Help: How come I can't use m(v^2/r)=kx for this problem?

  1. May 8, 2012 #1
    Relaxed spring is sitting on a horizontal surface. A block is attached at one of its ends is kicked with a horizontal velocity, v1, given to it. The block will move and stretch. Find the distance, x, the spring will stretch. X is in meters.

    Energy 1/2 mv1^2 = 1/2 mv2^2 + 1/2 k x^2
    Angular momentum mv1l0 = mv2(l0+x)

    The problem was solved using kinetic energy and conservation of angular momentum formulas.

    My question is, why doesn't m(v^2/r)=kx apply for this problem? Is it because m(v^2/r) is to only be used in uniform circular motion and the object in the problem moves in the shape of an ellipse?
  2. jcsd
  3. May 8, 2012 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I have no idea what path this thing moves on, but if the string stretches, then it can't be a circle.
  4. May 8, 2012 #3
    understood, but does m(v^2/r) only apply to a circle?
  5. May 8, 2012 #4
  6. May 8, 2012 #5
    thank you!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook