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## Homework Statement

A 20.0 m long uniform beam weighing 670 N is supported on walls A and B, as shown in Fig. 9-77.

http://www.webassign.net/giancoli5/9_77.gif

(a) Find the maximum weight a person can be to walk to the extreme end D without tipping the beam.

(b) Find the forces that the walls A and B exert on the beam when the same person is standing at point D.

(c) Find the forces that the walls A and B exert on the beam when the same person is standing at a point 2.0 m to the right of B.

(d) Find the forces that the walls A and B exert on the beam when the same person is standing 2.0 m to the right of A.

I figured out A + B but not C and D.

## Homework Equations

sigma Fy = 0

sigma FTorque = 0

## The Attempt at a Solution

FA = beam A

FB= beam B

mg= mass of beam * 9.8

FC= the person

a) 670N

b) 0 N from wall A and 1340N from wall B

C) using FA as the pivot: 0FAsin90 + 12FBsin90 -8.5mgsin90 - 15FCsin90 = 0

12FB - 15745 = 0

FB = 1312.08 WHICH IS NOT CORRECT.

D)