What Is the Correct Tension in Each Wire Holding Up the Light Fixture?

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Homework Help Overview

The problem involves a light fixture suspended by two wires, each making a 40-degree angle with the ceiling, and exerting a downward force of 80N. Participants are discussing how to determine the tension in the wires based on the forces acting on the system.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to use trigonometry to find the tension, initially assuming a direct upward force of 80N and splitting the triangle formed by the wires. They question their approach after receiving feedback from a software tool.
  • Some participants suggest resolving the forces acting on the system, particularly focusing on the components of tension in relation to the angles and the total force exerted by the fixture.

Discussion Status

Participants are actively exploring different methods to calculate the tension in the wires. There is a recognition of the need to resolve forces and consider the angles involved. One participant has acknowledged a successful adjustment to their calculations based on feedback received.

Contextual Notes

There is a mention of a software tool providing feedback on the calculations, indicating that participants are working within a structured homework context. The original poster's assumptions about the forces and angles are being scrutinized and discussed.

wetcarpet
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There are two wires connected to a ceiling with a light fixture hanging at their ends. The light fixture exerts a force of 80N, while the wires make a 40 degree angle with the ceiling. What is the tension in the two strings? The diagram roughly looks like this:

---------------
- 40 40 -
- -
- -
-
-
80N

I assumed that this was a simple trigonometry problem and set about solving it like so:
{a} I assumed that since the object was not moving downward, there had to be an 80N force exterted upward. Hence, I split the large triangle into two parts using a positive 80N force, making a 90 degree angle with the ceiling, and a 50 degree angle at the base of the larger triangle.
{b} From there I used trigonometry:
cos(50) = 80N/Hyp.
Hyp. = 80N/cos(50)
Hyp. = 124.5N

Yet, the software (Webassign.com) is telling me that the tension is not 124.5N. What am I doing wrong?

P.S.- I also tried assuming that there is not an 80N positive force exerted upward, and thereby tried isolating each X and Y vector for each string separately. I still got the same answer of 124.5N.
 
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If they want the value for T in each string, you need to divide that value by 2. Resolve the forces perpendicular to the string and you get 2Tsin 40 = 80.
 
I thank you kindly, dividing 124.5N by two did work, and I appreciate your explanation as well. :smile:
 
Last edited:

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