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Homework Help: Friction Problem

  1. Mar 23, 2005 #1
    The question is a 50g golf ball rolls horizontally to a stop in 30 cm of rough grass, as it just misses the green. The ball was moving at 10km/h [east] as it entered the rough grass. What is the frictional on the ball during the slowing down? Assume it was unifrom. Include an FBD and neglect gravity.????

    How do you find friction??
  2. jcsd
  3. Mar 23, 2005 #2
    Draw a free body diagram, identify that the only force acting is friction. The problem tells you that it took 30cm for the ball to stop.

    Think of an equation that relates Force, distance, velocity and mass.

    I can think of two.
  4. Mar 23, 2005 #3
    I used the v2(squared)=v1(squared) +2a*d
    My accelration i got around -12.88m/s
    and for the friction i got 0.643N?? does this sound right??
    Last edited: Mar 23, 2005
  5. Mar 23, 2005 #4
    Have you tried energy?
  6. Mar 23, 2005 #5
    it was strictly a friction question, without using any energy methods, although they could have been used. Is my answer correct??
  7. Mar 23, 2005 #6
    Your measured acceleration times your mass should equal your friction.
  8. Mar 23, 2005 #7
    [tex]F*d = \frac{m*v^2}{2} [/tex]

    By conservation of energy.
  9. Mar 23, 2005 #8
    Do you know much about free body diagrams??
  10. Mar 23, 2005 #9
    we know everything about free body diagrams...:)

  11. Mar 23, 2005 #10
    [tex] \Rightarrow V_0 [/tex]
    [tex] \Leftarrow F_f, F_n [/tex]

    How do you put mroe than one letter in a subscript?
  12. Mar 23, 2005 #11
    alright, ill never never question your knowledge again :smile:

    well for the question first asked, i got a friction of 0.644N. So for the FBD would there be an arrow going left being the 0.644N and one right. The one right labeled something like F less then 0.644N since it is coming to a stop. It also says to neglect gravity so im not worry about that.
  13. Mar 23, 2005 #12
    Whozum, just use the {} signs like this

    [tex]a_{mama mia 2}[/tex]

  14. Mar 23, 2005 #13
    The only arrows you should have are the ones I showed above

    [tex] \Rightarrow V_0 [/tex]
    [tex] \Leftarrow F_{friction}, F_{net} [/tex]

    You may not even need the [tex] F_{net} [/tex]

    There is only one force acting, the force of friction, and it is directed to the left, opposite the direction of motion. There is nothing pushing the ball to the right.
  15. Mar 23, 2005 #14
    Then what does the V0 stand for ?? and doesnt the ball still have the force on it from before when it was hit?? or i guess the question means right then, so just friction? ok, that makes sense then
  16. Mar 23, 2005 #15
    vo is the initial velocity

  17. Mar 23, 2005 #16
    alright, thanx for all your help marlon and whozum!!! :smile:
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