Torque and center of mass question

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Homework Help Overview

The discussion revolves around a problem involving torque and the center of mass of a block with non-uniform density suspended by two massless wires at different angles. The original poster attempts to find the center of mass using torque equations derived from the forces exerted by the wires.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the setup of the problem, including the placement of the fulcrum and the attachment points of the wires. The original poster shares their calculations and expresses confusion about the correctness of their answer, prompting questions about trigonometric considerations.

Discussion Status

The discussion is ongoing, with participants seeking clarification on the problem's setup and the original poster's reasoning. Questions about the placement of the fulcrum and the attachment of the wires indicate a collaborative exploration of the problem's assumptions.

Contextual Notes

There is a mention of the block having a non-uniform density, which may affect the center of mass calculation. The original poster's calculations are based on specific assumptions about the forces and angles involved, which are currently under scrutiny.

ktpr2
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We have a block of un-uniform density of mass m suspended by two massless wires, against gravity. The left wire makes an angle phi_1while the right angle makes an angle phi_2. The block has length L. They want me to find the center of mass.
THis is what I've done:
We have tension in the wires. Torque is force measured from a distance. In our case, the two wires create a torque about the center of mass. I find the forces,
F_1 = sin(phi_1)*m*g
F_2 = sin(phi_2)*m*g
And realize that the torques are
t_1 = F_1*x_c_m;
t_2 = F_2*(L - x_c_m)
since they equal another (net torque is zero), i set them t_1 = t_2 and solve for x. However the answer is incorrect and I am told to check my trignometry. My answer is
x = (L sin(phi_2)) / (sin(phi_1)+sin(phi_2))

whatever am i doing wrong?
 
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Where do you put your fulcrum?
 
my fulcrum is x_cm, or the center of mass of the block from the left side.
 
One question... are the wires attached to the ends of the block, you were not clear on that...
 
yes they are. the wire making an angle phi_1 is on the left side and the wire making an angle phi_2 is on the right side.
 

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