Calculating Moment Arm for a Force: Explained and Solved

[mathdude88]

Homework Statement

Homework Equations

T=Fl

The Attempt at a Solution

I'm not sure what the moment arm of this problem is. I think it is suppose to be a line connecting 0 to F1 at a right angle. To draw this moment arm one would have to extend F1 past where it meets A. However I am not sure is that is the right moment arm, how to find that distance, or how the other forces come into play for this problem.

 

[PhanthomJay]

Homework Statement

Homework Equations

T=Fl

The Attempt at a Solution

I'm not sure what the moment arm of this problem is. I think it is suppose to be a line connecting 0 to F1 at a right angle. To draw this moment arm one would have to extend F1 past where it meets A. However I am not sure is that is the right moment arm, how to find that distance, or how the other forces come into play for this problem.

The problem is asking for the moment about O of F1, so don't worry about the other forces. You are correct in that you can extend the line of action of force F1 and determine the perpendicular distance from that extension to point O, but that's too much geometry and trig. Alternatively, you can break up F1 into its x and y components, and calculate the moment arm and moment of each component about O (the moment from its y component should be 0 (Why?), so you just have to deal with the x component moment.). Or you can just use the cross product rule for torques, if you can determine the correct angle and position vector to use.

 

[thomate1]

The moment arm is the perpendicular distance from the point of rotation (or axis) to the line of action of the force. In this problem, the moment arm would be the distance from point A to the line of action of F1. This can be found by drawing a line from point A that is perpendicular to F1. The length of this line would be the moment arm.

To find the moment arm for other forces, you would follow the same process - draw a line from the point of rotation to the line of action of the force, and find the perpendicular distance between them.

Once you have the moment arm for each force, you can use the equation T=Fl to calculate the torque (T) created by each force. Remember that torque is a vector quantity, so you will need to consider the direction of the force and the direction of the moment arm when calculating the torque.

I hope this helps to clarify the concept of moment arm and how it relates to calculating torque in this problem. Good luck with your homework!