12.64. Model: Model the beam as a rigid body. For the beam not to fall over, it must be both in translational equilibrium net(0N)F=GGand rotational equilibrium netNm).τ=Visualize:The boy walks along the beam a distance x, measured from the left end of the beam. There are four forces acting on the beam. 1Fand 2Fare from the two supports, ( )GbFGis the gravitational force on the beam, and ()GBFGis the gravitational force on the boy. Solve:We pick our pivot point on the left end through the first support. The equation for rotational equilibrium is Gb2GB() (2.5 m)(3.0 m)()0 N mFFFx−+−=222(40 kg)(9.80 m/s )(2.5 m)
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