Find Maximum mass with the principles of torque and rotational equilibrium

  • #1
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.
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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.
 

Answers and Replies

  • #2
36
0
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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