The force of magnitude F acts along the edge of the triangular plate

In summary, the conversation is about determining the moment of a force about a point using the equation M=rxF. The participants discuss the method of finding the angle and components of the force vector, as well as the position vector starting at the chosen moment point. The expert reminds the participants that it is not allowed to solve the homework for them, but can provide guidance and clarification.
  • #1
pyroknife
613
3

Homework Statement


I attached the drawing.
The force of magnitude F acts along the edge of the triangular plate. Determine the moment of F about point O.

Homework Equations



M=rxF

The Attempt at a Solution


What I did was I just picked the top left point of the triangle and labeled that (0,h) which give me my r vector 0i+hj. After that I really don't know how to proceed except to find the angle by doing inverse tangent of h/b, but I just keep getting variable after variable. What other way is there to do this?
 

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  • #2


pyroknife said:

Homework Statement


I attached the drawing.
The force of magnitude F acts along the edge of the triangular plate. Determine the moment of F about point O.

Homework Equations



M=rxF

The Attempt at a Solution


What I did was I just picked the top left point of the triangle and labeled that (0,h) which give me my r vector 0i+hj. After that I really don't know how to proceed except to find the angle by doing inverse tangent of h/b, but I just keep getting variable after variable. What other way is there to do this?

F is

b i - h j

what matters is the y direction for it is perpendicular and x is forming no moment

you just (bi) cross (-hj) to get ( -bh ) k, a vector of bh magnitude into the page.
 
  • #3


The answer is supposed to be Fbh/(h^2+b^2)^.5. Answers do vary tho according to method, but I don't think yours matches this
 
  • #4


pyroknife said:
The answer is supposed to be Fbh/(h^2+b^2)^.5. Answers do vary tho according to method, but I don't think yours matches this

YES sorry I made a very Fundamental mistake and will try to rectify it


F= F *( b / ( h**2+b**2 ) ** 0.5 ) i + F*( h / ( h**2+b**2 ) ** 0.5 ) j

Fx * h = is the answer F*b*h *(h**2+b**2 ) ** -0.5

which is into the page
 
  • #5


I'm still a little confused. I would like to do all moment problems by using M=rxF. How would that work in this problem. i can get the F vector but it's going to look really messy because I got to define the angle theta as tangent inverse of (b/h) then take the cosine of the tangent inverse of (b/h) to get the x component and same for the y.
 
  • #6


pyroknife said:
I'm still a little confused. I would like to do all moment problems by using M=rxF. How would that work in this problem. i can get the F vector but it's going to look really messy because I got to define the angle theta as tangent inverse of (b/h) then take the cosine of the tangent inverse of (b/h) to get the x component and same for the y.


M=r X F is already defined to be M= ( rx i + ry j + rz k ) X ( Fx i + Fy j + Fz k )

here simply r X ( Fx i + Fy j ) = r X Fx i + rXFy j by distribution property

but here : r= h j what do you get when you cross j by j ? for the latter part, of course a zero

here rXFyj drops and we are left with r X Fx i , here you cross jXi which points in the direction into the page.
 
  • #7


stallionx said:
M=r X F is already defined to be M= ( rx i + ry j + rz k ) X ( Fx i + Fy j + Fz k )

here simply r X ( Fx i + Fy j ) = r X Fx i + rXFy j by distribution property

but here : r= h j what do you get when you cross j by j ? for the latter part, of course a zero

here rXFyj drops and we are left with r X Fx i , here you cross jXi which points in the direction into the page.

its so hard to write all this online w/o subscripts and stuff. can r=b i too?
 
  • #8


pyroknife said:
its so hard to write all this online w/o subscripts and stuff. can r=b i too?

Sir,

r is starting from ( 0, 0 ) ---> take origin

and

draw a vector to the APPlication point of F.

r begins at ( 0,0 ) ends at application point of F.
 
  • #9


stallionx said:
Sir,

r is starting from ( 0, 0 ) ---> take origin

and

draw a vector to the APPlication point of F.

r begins at ( 0,0 ) ends at application point of F.

what I asked was basically the ending point can be any point on the line of action right?
 
  • #10


pyroknife said:
what I asked was basically the ending point can be any point on the line of action right?

No Sir, position vector starts at wherever you take the moment ( here (0,0) ) with respect to, and ends at starting point of F. ( which is h units above the (0,0)
 
  • #11


stallionx said:
YES sorry I made a very Fundamental mistake and will try to rectify it


F= F *( b / ( h**2+b**2 ) ** 0.5 ) i + F*( h / ( h**2+b**2 ) ** 0.5 ) j

Fx * h = is the answer F*b*h *(h**2+b**2 ) ** -0.5

which is into the page

You need to stop doing the student's homework for them. You may provide hints, ask questions, find mistakes, etc. But it is against teh PF rules to do the student's work for them.
 

What is the force of magnitude F?

The force of magnitude F is a measurement of the strength or intensity of a force acting on an object. It is typically measured in units of newtons (N).

What does it mean for a force to act along the edge of a triangular plate?

This means that the force is applied in a direction that is parallel to one of the edges of the triangular plate. This can also be described as the force being applied tangent to the edge of the plate.

How is the force of magnitude F calculated?

The force of magnitude F is typically calculated using the equation F = ma, where F is the force, m is the mass of the object, and a is the acceleration. However, in the case of a triangular plate, the force may also be calculated using trigonometric principles.

What factors can affect the force of magnitude F?

The force of magnitude F can be affected by several factors, including the mass and acceleration of the object, as well as any external forces acting on the object. Additionally, the angle at which the force is applied can also affect its magnitude.

What is the significance of the force of magnitude F acting along the edge of a triangular plate?

The force of magnitude F acting along the edge of a triangular plate can have implications for the stability and movement of the object. It may also be used in engineering and physics to analyze and understand the behavior of structures and objects under different forces.

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