# Homework Help: Fracture and shear forces on a beam

1. Nov 9, 2009

### itsalwysunny

1. The problem statement, all variables and given/known data

A 20.0 meter long uniform beam weighing 820 N rests on walls A and B, as shown in the figure
a)Find the maximum weight of a person who can walk to the extreme end D without tipping the beam.

b)Find the force that the wall A exert on the beam when the person is standing at D.

c)Find the force that the wall B exert on the beam when the person is standing at D.

d)Find the force that the wall A exert on the beam when the person is standing at a point 2.0 meters to the right of B.

e)Find the force that the wall B exert on the beam when the person is standing at a point 2.0 meters to the right of B.

f)Find the force that the wall A exert on the beam when the person is standing 2.0meters to the right of A.

g)Find the force that the wall B exert on the beam when the person is standing 2.0meters to the right of A.

3. The attempt at a solution

i know that for the person to reach the far end of D without the beam tipping the weight of the man W_m has to equal the forces acting on the beam at the spot of the two supports. I know the sum of the forces is equal to zero so i tried working out the weight at each end multiplied by its corresponding x position and set it equal to zero in order to find the weight of the person but came out with the wrong solution. Any idea how to go about doing the problem?

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2. Nov 10, 2009

### ideasrule

Have you tried torques? Total torque must be 0 if the beam is to balance.