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!

Free Body Diagram and applied force

  1. Jan 28, 2013 #1
    1. The problem statement, all variables and given/known data

    A cavewoman is dragging her 65.4 kg mate home, up a gentle 10° incline. The co efficient of friction for skin on oil is 0.40. What is the minimum applied force she needs to keep the neanderthal moving with uniform motion?

    2. Relevant equations

    ff=μFn
    fg=mg
    fnet=ma

    3. The attempt at a solution

    I tried solving for Ff using ff=μFn but I don't have the Fn do I? We have gravity going down which is -9.8(65.4)=640.92...would that be the force of normal?
     
  2. jcsd
  3. Jan 28, 2013 #2
    f=ma
    I have mass but not acceleration? How would i calculate it?
     
  4. Jan 28, 2013 #3
    so...fa=65.4(0)...?
     
  5. Jan 28, 2013 #4
    it does not..thats my problem :S
     
  6. Jan 28, 2013 #5
    :/ Are you sure lol? I am pretty sure he prof wouldn't give a question thats not solveable
     
  7. Jan 28, 2013 #6
    ah alright, so prof musta made a mistake. Thanks, Got an exam tommorow though :P hope he doesnt put this question on it
     
  8. Jan 28, 2013 #7
    school in Calgary :P
     
  9. Jan 28, 2013 #8
    The professor didn't make a mistake.

    You already calculated the force of gravity acting on the guy. For a slope of 10 degrees, what are the components of this force in the directions perpendicular and parallel to the incline? What direction does the force parallel to the incline point (up the incline, or down the incline)? If she is trying to pull the guy up the incline, what frictional force does she have to overcome? Make a list of the forces acting on the guy parallel to the incline. How many forces are there? According to the problem statement, is the guy accelerating up the incline, or is he just barely moving at a constant speed?

    Chet
     
  10. Jan 28, 2013 #9
    - Frictional Force, Moving towards the left
    - Force applied going [E 10 N]
    - Force of Gravity Down
    - Force of Normal Up

    Since it says gently, I assume it is moving at a constant velocity? or close to?

    What is the next step after Force of gravity?

    Thanks for replying Chet
     
  11. Jan 28, 2013 #10
    The gravitational force acting on the guy can be resolved into two components, one perpendicular to the incline and the other parallel to the incline. What are the numerical values of these two components?
     
  12. Jan 28, 2013 #11
    component y = -9.7?
    Component x = Force of friction ? That is the only force acting in the x direction isn't it?
     
  13. Jan 28, 2013 #12
    I can't figure it out :/
     
  14. Jan 28, 2013 #13

    SammyS

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    What do you mean by "the x direction"? If that is along the surface of the incline, then there is a force in addition to friction acting in the x direction, namely gravity. Gravity has a component along the incline.
     
  15. Jan 29, 2013 #14
    You already said that the gravitational force acting on the guy is 641 N. Do you know how to resolve this force into components perpendicular and parallel to the 10 degree incline?

    Gravity doesn't exert any frictional force on the guy. The frictional force is exerted on the guy by the inclined plane. But we will get to that later.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook