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 8.98 m work plank which weighs 115 N and is secured with a hinge on the opposite end. Worker B will stand on the plank 4.55 m from worker A. Worker B also brings up his paint can, mc = 3.56 kg, which he places 0.280 m from where he is standing on the plank (between the two workers). Worker A unfortunately needs to supply 509 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

From sum the moments about the hinge is zero

sigma M = 0

0 = ( 509 * 8.98 ) - (115 * 8.98/2) - WB (8.98 - 4.55) - 3.56 * 9.81 * (8.98 - 4.55 + 0.280)

4.43 WB = 3890

worker B weigh WB = 878 N

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