Question

Consider a rigid steel beam of length L = 13.5 m and mass mb = 398 kg resting on two supports, one at each end. A worker of mass mw = 78 kg sits on the beam at a distance x from support A. Refer to the figure.

(A В L

1) When the worker sits at a distance x = 1.5 m from support A, calculate the force, in newtons, that support B must exert on the beam in order for it to remain at rest. Use g with three significant figures.

2) The force exerted on the beam by support A is measured and found to be F_A = 2360 N. At what distance x, in meters, from support A is the worker sitting now?

Answer 1

mw mb RA muy mog RB L = 13.5m My = 398 kg mw = 78 kg x=1.5m g= 9.806 mg RB = 1 Taking moment about A, Mnet zo clockwise is the OXRA ot xxm wg + L mog - LXRB = 0 2 si 1.5x 78 x 9.806+ 13.5x398x9-806 .13-5X RB=0 V. RB = 2036.3793 N 2) RA = 2360 N Taking moment about B, Mneto LXRA - (L->) mwg - L mogaº 2

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