Statics question about moments

[hockeyguy314]

Homework Statement

Find the components of the force at D and C using moments

picture attached

Homework Equations

M=F x r

The Attempt at a Solution

I'm really stuck on this one. The force from the 70 kg weight is 70*9.8 = 686N, so F=-686j. I found the moment about point C to be M_c=1715k. After that, I'm not sure where to go. I'm also really thrown off by the white line that's at a 60° angle below the x axis. Any help would be greatly appreciated. Thanks.

 

[pongo38]

It looks to me that the white line is an arrow representing the force required to keep the device in equilibrium. Does that help?

 

[hockeyguy314]

Yes, it does help thank you. I still don't know where to go from here though. I guess I'm not really sure how the moment about C would translate into components of force.

 

[pongo38]

Well, do you not know enough to be able to calculate the white force itself, even if you don't know its components?

 

[rezeew]

As a scientist, it is important to approach problems systematically and logically. In this case, we are dealing with moments, which are a measure of the rotational effect of a force. The equation for moments is M = F x r, where F is the force and r is the distance from the point of rotation.

To find the components of the force at D and C, we can start by drawing a free body diagram of the system. This will help us visualize the forces and their directions.

Next, we can use the moment equation to find the moment at point D, which is the sum of the moments of all forces acting on the system. This can be done by taking the cross product of the force at D (Fd) and its distance from point D (rD).

Similarly, we can find the moment at point C by taking the cross product of the force at C (Fc) and its distance from point C (rC).

Now, we have two equations (Md and Mc) and two unknowns (Fd and Fc) which can be solved using basic algebra.

The white line at a 60° angle below the x-axis is a reference line to help us visualize the forces and their directions. It does not affect the calculations, as long as we are consistent with our coordinate system.

I hope this helps guide you in the right direction. Remember to always approach problems systematically and don't hesitate to seek help when needed.