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Ladder leaning on wall, person on ladder.

  1. Oct 12, 2014 #1
    http://ronney.usc.edu/AME101/AME101-F14-PS3.pdf [Broken]

    number 1 in the link tyty
     
    Last edited by a moderator: May 7, 2017
  2. jcsd
  3. Oct 12, 2014 #2

    Matterwave

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    Please use the template provided, and also show what you did to try to solve the problem.
     
  4. Oct 12, 2014 #3
    ohhh my bad
     
  5. Oct 12, 2014 #4
    uhh how do i get the template now?
     
  6. Oct 12, 2014 #5

    Matterwave

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    You can start a new thread in another window and just copy and paste the template over to here.
     
  7. Oct 12, 2014 #6
    anyways naming the point of where ladder touching the wall 1 and the part where the ladder touches the ground 2 I have
    Fn1 will the wall's force on the ladder and Fn2 will be the ground's force on the ladder. Ffr1 is friction of where 1 is and Ffr2 is friction force of where 2 is.

    Sum of Fx= Fn1 - Ffr2=0 Fn1=Ffr2
    Sum of Fy=Ffr1+Fn2=0=Ffr1+Fn2-150

    then I'm not sure what to do.
     
  8. Oct 12, 2014 #7
    hmm i did try your way but it's not giving me the template anymore
     
  9. Oct 12, 2014 #8
    ahh found it

    1. The problem statement, all variables and given/known data
    to find all unknowns.
    mu2=0.24
    distance from person to 1 is 3ft
    distance form person to 2 is 7ft
    horizontal distance is 4ft
    mg of individual is 150lbf

    2. Relevant equations
    torque=fd

    3. The attempt at a solution
    Sum of Fx= Fn1 - Ffr2=0 Fn1=Ffr2
    Sum of Fy=Ffr1+Fn2=0=Ffr1+Fn2-150
     
  10. Oct 12, 2014 #9

    Matterwave

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    EDIT: looks like you found it.

    I see that your relevant equations has a torque equation in it, and yet you did not attempt to use it in your solution. Why is that?
     
  11. Oct 12, 2014 #10
    oh sorry I did try taking moments in both point 1 and point 2 and turned out with nothing.

    Taking moment at point 1.
    M1=-(3(150))+Fn2(10)

    Taking moment at point 2
    M2=-(Fn1(10)+(7(150))

    Taking moment at where the person is at
    M3=-Fn1(3)+Fn2(7)

    From there on I'm not sure what to do
     
  12. Oct 13, 2014 #11

    Matterwave

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    Your moment equations are incorrect because they don't take into account the angle between the force and the radius displacement. The correct equation for torque is ##\vec{\tau}=\vec{r}\times\vec{F}##

    Also, at point 1 (and at point 2), there are 2 different forces, the frictional force and the normal force. You have to take both of them into account.
     
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