- #1

lightlightsup

- 95

- 9

- Homework Statement
- See image for question from: Fundamentals of Physics - 10E - Page 346 - Chapter 12 - Problem 21 (YouTube: y2u.be/ZY3-ZSQP1Mo).

- Relevant Equations
- For Part A, I was able to figure out the τ components around the hinge and solve for T. The τ parts are mostly intuitive for me in these problems.

Parts B and C confused me (though I solved them with YouTube help (see above)).

I'm having trouble developing intuition around ΣF=ma=0 in statics. Specifically, with regards to Normal or Reaction Forces.

My explanation for Parts B and C right now is:

Since the strut is not rotating (Στ(strut's bottom) = 0), all those forces on it will be directed down the strut and towards the hinge.

In this case, the downward Fg(block), Fg(strut), and the downward component of the T are all pushing down on the strut which is pushing into the hinge. The hinge responds with an equal force in the opposite direction (upward). So, we have no translational motion in the y direction.

The horizontal (-x, left) component of the T travels down the strut and tries to pull the hinge leftward (-x), but, once again, the hinge responds with an equal force in the opposite direction (rightward, +x) and so, we have no translational motion in the x direction.

Is this correct?

Does anyone have a more intuitive explanation or something I could watch or read to develop my intuition here? I know that not everything in physics has intuitive explanations but it's worth a try.

It just baffles me that I don't have to consider how far the block is from the hinge/strut connection when doing ΣF=0.

I know the general principles here are that:

ΣF(anywhere) = 0

Στ(anywhere) = 0

So, in a statics problem, since Στ(somewhere) = 0, then, I've got to trust that all those would be τs are being directed purely into ΣF=ma? I don't have to care about the distance from the point being considered during ΣF=ma? All the τs that would have gone into changing L are going to be re-directed into ΣF=ma (=0 due to a reaction force)?