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April 23, 2014

Homework Help: Physics help.

Posted by Lilly on Tuesday, February 21, 2012 at 5:20pm.

The 78.0 kg climber is supported in the "chimney" by the friction forces exerted on his shoes and back. The static coefficients of friction between his shoes and the wall, and between his back and the wall, are 0.840 and 0.630, respectively. What is the minimum normal force he must exert? Assume the walls are vertical and that friction forces are both at a maximum. Ignore his grip on the rope.

78*g*.63=F1
78*g*.84=F2

F1+F2=78*g

F2-F1=78*g*(.84-.63)

F2=78*g-F1

78*g-2*F2=78*g*(.84-.63)
F2=78*g*(1-.84+.63)/2

F2= 302 N
F1= 463 N

I thought the answer was 302N but the homework website is telling me that I am wrong. Where did I mess up?

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