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Homework Help: Finding Force of an Object on Incline w/ Constant Speed & Coefficient

  1. Oct 6, 2012 #1
    1. The problem statement, all variables and given/known data

    Hi guys and gals,

    Having an issue with this one and was hoping to get some help. I'm going to write out the equation and include an attachment with my free body diagram.


    How long a force parallel to a 20° hill does it take to push a 100-lb box up the hill at a constant speed of 30 ft/s if the coefficient of the kinetic friction between the box and the hill is 1/3.

    2. Relevant equations

    F=ma fk=uk(Fn) w=mg m=w/g v=30ft/s

    3. The attempt at a solution


    I just can't seem to wrap my head around this one. There really isn't a good explanation in the book. I've included my free body diagram. Thanks for the help.

    Attached Files:

  2. jcsd
  3. Oct 6, 2012 #2
    Okay just did it on a paper and snapped a pic of it.


    It appears not clear enough with flash >.<
  4. Oct 6, 2012 #3
    So is there no numerical answer? Or just variables?
  5. Oct 6, 2012 #4
    The idea is there are still forces acting on the objects, just that the net force (sum of all) is zero.
    So your upward force is equal to your downward ones.
  6. Oct 6, 2012 #5
    Okay, yeah I figured that. As F=ma equals zero. I appreciate your help. Just wanted to make sure there wasn't something else that I was missing
  7. Oct 6, 2012 #6
    there is numerical answer...
    I'm lazy to calculate it. Just told you the concept,ask if I'm not stating clearly
    Try and post your calculations :)
  8. Oct 6, 2012 #7
    okay good luck haha
  9. Oct 6, 2012 #8
    I will try later. I got stumped, it's my last question for this week. I moved onto Chemistry. I will go back to it though and post.
  10. Oct 6, 2012 #9
  11. Oct 14, 2012 #10
    Sorry about the wait on this one. Been super busy learning new stuff. Below is the attachment to the solution.

    Attached Files:

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