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## Homework Statement

A 70kg climber is suppored in a "chimney" by the friction forces exerted on his back and shoes. The coeffcients of static friction of his feet against the wall and his back against the wall are 0.8 and 0.6 respectively. What is the minimum normal force he needs to apply to keep from slipping? Assume the walls are perfectly vertical and the the frictional forces are at impending slipping.

## Homework Equations

F=ma

Ff(frictional force)=mu*n(normal force)

W=mg

## The Attempt at a Solution

What I did was calculated the frictional force for the feet and the back using Ff=mu*n

What I came up with was aprox 980Newtons. Then I figured that since static friction is only used as needed, I calculated the climber's weight and I came up with 686N.

That doesn't sound right to me. What am I messing up? Thanks