Find Maximum mass with the principles of torque and rotational equilibrium

1. Nov 22, 2011

Leanna.Agahi

I need help with this physics problem! Please help I'm completely stuck.

A beam 3m long is free to pivot up and down about the end attached to a wall. The mass of the beam is 25 kg and the cable supporting the beam can support a maximum force of 1800 N. What is the maximum mass that a man standing on the end can have before he snaps the cable. The angle of elevation between the cable and the beam is 30 degrees.
?

I tried converting the 25 kg to newtons, therefore getting me 245N and subtracting that from the 1800 (which I thought would be the easy way) and then dividing by 9.8 to get the mass in kg, but that ended up being incorrect.

The correct asnwer is 79.3 Kilograms, but I would enjoy to know how to get to that conclusion.

2. Nov 23, 2011

LabGuy330

You are almost correct except one thing, you forgot the angle of the cable relative to the beam.

redo your equation by summing the forces in the Y direction (1800N is not in the Y direction)

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