Having trouble with this Moments about the coordinate axes problem

In summary, the problem involves finding the moment M_y of a force F applied to a valve about the y axis, given that the moments of the force about the x and z axes are -77 lb ft and -81 lb ft, respectively. The formulas for calculating the moments are provided, but the difficulty lies in finding the components of the force. The given x, y, and z values are incorrect as they are in inches and need to be converted to feet. Additional equations may be needed to solve for the component of the force.
  • #1
btbam91
91
0
Having trouble with this "Moments about the coordinate axes" problem!

When a force F is applied to the handle of the valve shown, its moments about the x and z axes are, respectively, M_x= -77 lb ft and M_z= -81 lb ft. For d=27 in., determine the moment M_y of F about the y axis.
[PLAIN]http://img411.imageshack.us/img411/8366/092310015800.jpg

I figure I'm supposed to use the formulas:

M_x= yF_z - zF_y
M_y= zF_x - xF_z
M_z= xF_y - yF_x

but I'm having trouble on finding a component of the force.

Also, are my x,y,z's correct??

I got, x=-4, y=11, z=-27

Thanks!
 
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  • #2


Sorry for the large picture, right click>view image for a better view of it!
 
  • #3


im working on this same problem and i can't figure it out at all. all i know is that your x,y,and zs are wrong. you are given the moments with units of ft.*lbs. and those numbers are inches, so you need to divide them by 12 to make them feet.

i managed to express M_y in terms of F_y but idk how to solve for F_y. its still in terms of F and theta. there must be more equations to use that we arent thinking of.
 

Related to Having trouble with this Moments about the coordinate axes problem

1. What is a moment about the coordinate axes?

A moment about the coordinate axes is a measure of the tendency of a force to rotate an object around a specific axis. It is calculated by multiplying the magnitude of the force by the perpendicular distance from the axis to the line of action of the force.

2. How do I calculate the moment about the coordinate axes?

The moment about the coordinate axes can be calculated using the equation M = F*d, where M is the moment, F is the force, and d is the distance from the axis to the line of action of the force. Make sure to use consistent units for both force and distance.

3. What is the difference between moment about the x-axis and moment about the y-axis?

The moment about the x-axis is the tendency of a force to rotate an object around the x-axis, while the moment about the y-axis is the tendency to rotate around the y-axis. The x-axis and y-axis are perpendicular to each other and intersect at the origin (0,0) on a Cartesian coordinate system.

4. Can a moment about the coordinate axes be negative?

Yes, a moment about the coordinate axes can be negative. This occurs when the force is directed in the opposite direction of the rotation, or when the distance from the axis to the line of action of the force is negative. It is important to pay attention to the direction of the force and the sign convention when calculating moments.

5. How can I use moments about the coordinate axes in real-world applications?

Moments about the coordinate axes are commonly used in engineering and physics to analyze and design structures, machines, and other mechanical systems. They can also be used to determine the stability of an object and predict its behavior under different forces and loads.

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