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: Work / Nonconservative Force

  1. Dec 7, 2007 #1
    1. The problem statement, all variables and given/known data
    A .190 kg block is compressing a spring k = 200 N/m for a dist. of .15m. The spring is mounted horizontally and the surface directly under it is frictionless. But beyond the equilibrium position of the spring end, the surface has a coefficient of friction u = .27. The frictional surface extends 85 cm, followed by a frictionless curved rise. After launch where does the block finally come to rest. MEasure from the left end of the frictional zone.

    2. Relevant equations

    3. The attempt at a solution
    Well the first thing I do is find the PE of the spring. PE = .5 k x^2 = 2.25 J
    Secondly, I figure out the Work caused the by the frictional patch. W = .190*g*.27*.85 = .427329 J

    Then I subtract them 1.82 J and this is where I get stuck, since I don't know the curvature of the curve, how am I supposed to figure out when it comes to rest? I can figure out the velocity at the end of the patch and I can also figure out the height from mgh = 1.82J, but that still doesn't take into account the curve... I've also thought about trying kinematic equations, but that doesn't seem to work either.
  2. jcsd
  3. Dec 7, 2007 #2
    Perhaps you are answering your own question, in that you can determine the height above the flat plane the block would rising using mgh. Without any additional information regarding the curve I think that answer would suffice.
  4. Dec 7, 2007 #3

    I didn't run through your numbers, so not sure if they're accurate or not, but I wanted to say that seeing as you don't know how curved the curved rise is, I think its perfectly acceptable to express your answer in terms of height off of the ground. You could go further, and assume a constant curvature, and calculate the distance based on the radius of curvature or whatever, but I don't really see how that's any more rigorous or accurate than expressing it as height off of the ground.

    But I don't know your teacher, so YMMV :P That kind of ancillary calculation after the fact seems immaterial to the physics concepts being asked here, IMHO.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook