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

Question

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 8.00 m work plank which weighs 111 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, m_c = 3.56 kg, which he places 0.445 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/s^2.

Explanation / Answer

Sum the moments about the hinge:
M = 0 = 522N*8.00m - 111N*8.98m/2 - B*(8.00-4.55)m
- 3.56kg*9.81m/s²*(8.00-4.55+0.445)m
B * 4.55m = 3915 N·m
B = 955 N

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