Why Did I Get the Wrong Answer for the Force at Point C?

In summary, the conversation is about finding the force at C in a given problem solution. The person asking the question initially attempted to solve it by summing moments about point B, but got the wrong answer. Another person points out that the angle denoted as 5 degrees may actually be 15 degrees, and that summing moments about B may not work since C has both vertical and horizontal components. The first person then realizes their mistake and reorients BD to have a 5 degree angle, but is still unsure if force C will be perpendicular to BD. They further explain that they summed the moments about B using given answers and converted forces C and P to be perpendicular to BD, but the resulting moment does not equal zero. They
  • #1
theBEAST
364
0

Homework Statement


Here is the question along with part of the solution. I am online concerned about finding the force at C.

KYAZc.png


The Attempt at a Solution


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For my solution I decided I would sum the moments about point B. However I ended up getting the wrong answer for the force at C. Does anyone know why?
 
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  • #2
You didn't follow the solution manual. You should first check your geometry to see that the angle you denote as 5 degrees is actually 15 degrees. But then if you sum moments about B, C has both vertical and horizontal components, it is not perpendicular to the member.
 
  • #3
PhanthomJay said:
You didn't follow the solution manual. You should first check your geometry to see that the angle you denote as 5 degrees is actually 15 degrees. But then if you sum moments about B, C has both vertical and horizontal components, it is not perpendicular to the member.

Ah, I reoriented BD so that the angle there is 5 degrees instead of 15 :P. So you are saying force C will not be perpendicular to BD?

I just summed the moments about B using their answers. I converted the forces C and P so that they are perpendicular to the link BD and summed the moments. The moment does not equal to zero. Is this an error?

Here is my work:
brCCN.png
 

FAQ: Why Did I Get the Wrong Answer for the Force at Point C?

What are moments about different points?

Moments about different points refer to the calculation of the turning effect of a force around a specific point or axis. It is a measure of the rotational force or torque on an object.

How do you calculate moments about different points?

To calculate moments about different points, you need to multiply the force acting on an object by the perpendicular distance from the point to the line of action of the force. This can be represented by the equation M = F x d, where M is the moment, F is the force, and d is the distance.

What is the difference between a positive and negative moment?

A positive moment creates a counterclockwise rotation around the point, while a negative moment creates a clockwise rotation. This is determined by the direction of the force and the direction of the distance from the point.

How does the distance affect the moment?

The distance affects the moment by increasing or decreasing the rotational force on an object. The longer the distance, the greater the moment, and the shorter the distance, the smaller the moment. This is why a longer wrench can provide more torque than a shorter one.

What are some real-life applications of moments about different points?

Moments about different points are important in many fields, from engineering to sports. In engineering, they are used in the design of bridges, buildings, and machines to ensure structural stability. In sports, moments are utilized in techniques such as throwing, swinging, and skating to generate more force and improve performance.

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