A young work crew is trying to quickly finish some touch-up painting to complete

Question

A young work crew is trying to quickly finish some touch-up painting to complete a job. Rather than setting up a secure work area, they decide to try a shortcut. Worker A will hold the far end of a 9.47 m work plank which weighs 114 N and is secured with a hinge on the opposite end. Worker B will stand on the plank 4.77 m from worker A. Worker B also brings up his paint can, mc = 3.58 kg, which he places 0.385 m from where he is standing on the plank (between the two workers). Worker A unfortunately needs to supply 522 N of force to hold the end of the plank. How much does worker B weigh? The acceleration due to gravity is g = 9.81 m/s2.

Explanation / Answer

Balancing moments about the hinge,

522*9.47 = Wb*(9.47 - 4.77) + (3.58*9.81)*(9.47 - 4.77 + 0.385) + 114*(9.47/2)

Wb = 898.9 N (or 898.9/9.81 = 91.6 kg)

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