physics problem!!!?

Question

A 71 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 0.83 and 0.65, respectively. What is the minimum normal force he must exert? Assume the walls are vertical and that friction forces are both at a maximum.

Answer 1

Look at the frictional force by the back as F1 and the force of the shoes as F2
71*g*.65=F1
71*g*.83=F2

F1+F2=71*g

F2-F1=71*g*(.83-.65)

F2=71*g-F1

71*g-2*F2=71*g*(.83-.65)
F2=71*g*(1-.83+.65)/2
F2=285 N
F1=411 N

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