What is the magnitude of F required to raise the lamp post?

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Discussion Overview

The discussion revolves around determining the magnitude of force required to raise a lamp post by creating a counterclockwise moment of 1500 lb*ft about a specified point. The scope includes homework-related problem-solving and mathematical reasoning involving vector calculations and moments.

Discussion Character

  • Homework-related
  • Mathematical reasoning

Main Points Raised

  • One participant states the need to calculate the force required to create a specific moment but expresses uncertainty in performing the calculations.
  • Another participant inquires if the original poster is familiar with the cross product rule for determining moments.
  • A participant explains the formula for moments using the cross product, detailing the components involved, including the position vector, the applied force, and the angle between them, suggesting the use of the law of sines and cosines to find the angle.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus, as there is ongoing uncertainty regarding the application of the cross product and the calculations needed to determine the force.

Contextual Notes

The discussion highlights a lack of clarity on how to apply the cross product in this context and the need for further exploration of the relationships between the vectors involved.

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Homework Statement



In order to raise the lamp post from the position shown, the force on the cable must create a counterclockwise moment of 1500 lb*ft about point A. Determine the magnitude of F that must be applied to the cable.

Homework Equations



I can find the magnitude of a vector when I know the vector. Not in this problem.

The Attempt at a Solution



I know a fair amount to get started, such as definitions, but I have no idea how to actually do calculations.
 

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Are you familiar with the cross product rule for determining moments?
 
I'm familiar with the cross product, but not sure how to use it to determine moment.
 
M = r X F =rFsintheta, wher r is the magnitude of the position vector between the base of the post and the point of application of the force(the length of the post), F is the magnitude of the applied tensile force, ant theta is the included angle between the force and position vectors. You'll have to use the law of sines and cosines to first find theta.
 

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