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Torque-Sign hanging from a cable

  • Thread starter sam2k2002
  • Start date
10
0
Torque--Sign hanging from a cable

1. Homework Statement

A 120cm-wide sign hangs from a 5.4 kg, 200cm-long pole. A cable of negligible mass supports the end of the rod as shown in the figure

What is the maximum mass of the sign if the maximum tension in the cable without breaking is 330N?


http://session.masteringphysics.com/problemAsset/1070549/3/12.P66.jpg" [Broken]

2. Homework Equations
T = r*F*sin(phi) = F * d (d = moment arm length)


3. The Attempt at a Solution

I set the Torque provided by the tension in the cable equal to the torque provided by the weight of the sign because the cable will break when the mass is just above the mass at this point.

(330N)(2m)(sin 51) = (1.2m)(9.81)(max_mass)

with this I get the max_mass to = 43.6kg, a wrong answer. Can anyone help me out here? Thanks.
 
Last edited by a moderator:

PhanthomJay

Science Advisor
Homework Helper
Gold Member
7,114
456
What happened to the weight of the pole? What point are you summing torques about?
 

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