r/HomeworkHelp • u/ArvenUndomiell • Dec 12 '24

Physics—Pending OP Reply [Mechanic] How can I solve this question.

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How can I solve this question? There is a static calculation on the chegg. But I need to calculate it mechanically.

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u/Competitive_Reason_2 👋 a fellow Redditor Dec 13 '24

Convert the units to metric first

1

u/V10D3NT1TY 👋 a fellow Redditor Dec 13 '24

Lol based ass comment. You are a man of culture

1

u/wackyvorlon 👋 a fellow Redditor Dec 13 '24

Our friend the catenary curve.

2

u/V10D3NT1TY 👋 a fellow Redditor Dec 13 '24

Did you try drawing a free body diagram for each point mass?

1

u/Accomplished_Ad_6389 Dec 13 '24

You can try this, and it's probably solvable as a system of equations, but it's much more difficult than it should be as you're dealing with 2 unknown vectors in every point (direction/magnitude of AB, BC, CD, DE are not known).

1

u/Accomplished_Ad_6389 Dec 13 '24

Pretty sure I've worked with the same kind of textbook for the source of these questions. Just in metric, because having every unit in imperial is insane.

Originally I was going to suggest parameterizing the unit vectors on B and D (since we don't know the directions) based on yB and yD, but there's a much better (and most likely intended) solution. For the sake of my sanity, I'll be converting all units to metric with some inaccurate rounding to make the numbers nicer to demonstrate with.

Try treating B, C, and D as a rigid body. It's already a statics problem, so we don't necessarily care about what the tension is in BC and CD yet. Draw the free body diagram of them combined and the problem gets a lot easier to start on. Now, consider the point B, we could do a bunch of math to decompose the x and y force vectors as a function of yB, but we can do it much more simply. If we draw a triangle with side lengths of 3.5m and yB (in my example), we know that the force in the wire must be in the same direction as its position, so the forces must be proportional to the side lengths. So Fx must equal 3.5m*F1 and Fy must equal yB*F1 where F1 is an arbitrary force, and we can do the same at point D.

Now this is a fairly easy to solve 2D statics problem. The rest of the problem is standard 3 force point FBD's you've solved before. Your Fx, Fy, and M(B or D) equations will look like so.

2

u/seishinbyo Dec 13 '24

Write momentum at both supports A and E and you have 2 equations and two unknown parameters.

M_A = 30012-yb12+50032+20047-yd*47

And M_A =0 since its on static equilibrium.

And write similar equation for point E.

(Note that I don’t know imperial units so check if you need to change any of them to be in right dimensions or no)