Analysis of a system of bodies where all forces are in balance and there is no motion relative to a chosen reference frame.

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Problem solving moments in equilibrium

Two straight ladders, AC and BC, have equal weights $W$. They stand in equilibrium with their feet, A and B, on rough horizontal ground and their tops freely hinged at C. Angle CAB = 60$ ^o$, angle ...
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1answer
299 views

Choosing the right point when calculating moments

A body is composed of two straight pins that are joined at a right angle. They have lengths $a$ and $b$ and the mass per unit length is $\rho$. When the body is balanced on a flat surface, as shown, ...
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1answer
53 views

Torque in a 2-segment robot leg

I have a (hypothetical) robot with two legs, each with 2 segments, with a joint at the body of the robot and in the 'knee' of each leg, as in this (poorly-drawn) diagram: (Sorry about the quality and ...
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2answers
80 views

Does the distance two weights are from you alter the difficulty of lifting them?

If I am weightlifting and I choose to do the deadlift, does it matter how far away from me the weights are on the bar, given that they are equally distance from me on both sides. E.g. I am deadlifting ...
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6answers
3k views

Why does the weighing balance restore when tilted and released

I'm talking about a Weighing Balance shown in the figure: Press & Hold on onside of the horizontal beam and then release it. It makes some oscillations and comes back to equilibrium like shown ...
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3answers
4k views

How do I find the tension in additional strings in this problem? [closed]

A mass of 5.00 kg hangs attached to three strings as shown in the figure (see image below). Find the tension in each string. Hint: Consider the equilibrium of the point where the strings join. ...
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1answer
356 views

How is weight distributed when legs are astride?

Is there a simple and quick formula to find the weight (the force acting) on each leg, especially when legs are astride and they are not equally stretched? (or, better) not equally distant from the ...
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3answers
429 views

What is the equation for the tension on the ends of a cable suspended at different heights?

I'm looking for an equation to find the tension on the ends of a cable suspended between two poles (one higher than the other) with no load but the cable itself. I determined that the tension would ...
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1answer
577 views

Finding the mass of bed/Patient [closed]

One of my friends has a problem and we don't know how to get this done, We want to to know the mass of a patient who is laying on a bed. One scales was put under the foot of a bed and weighed 232kg ...
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1answer
41 views

Finding directions of the internal forces within a freely jointed rigid object?

Consider the the following problem: Here is a force diagram showing the situation: For part (i) Taking moments about $B$ for $BC$ gives $84.5Lcos\beta=2LT$ So $T=39$N For part (ii) Resolving ...
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1answer
188 views

Forces acting on two balls in a jar [closed]

Consider the following situation: Two balls are inside a jar with diameter $D$. The balls are uniform in mass and both have the same diameter $d$. Express the forces that acts at the colored dots ...
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3answers
345 views

Topple a mass standing still

Consider the following situation: This is taken from an example from my book with a solution. The box weight is $W$ and the coefficient of friction between the floor and the object is $\mu$. What ...
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2answers
39 views

A statics problem to find minimal friction

consider the following: I need to find the minimal coeeficient of friction $\mu _{min}$ so that both recatngle boxes would remain static. The lower angle in the triangle is $2\alpha$ as indicated. I ...
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1answer
333 views

Massive ropes and tension

Consider the diagram bellow, a massive string hanging in equilibrium My question is this: Can we take any 2 random point on the rope, say A and B and then use $\sum F=0$ on the rope between them: ...
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0answers
207 views

Torque of person on bridge [closed]

Consider a 10 meter bridge that weighs 500 N supported at both ends. A person who weighs 750 N is standing 2 m from the end of the bridge. What are the forces $F_a$, $F_b$ holding the bridgeup at ...
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1answer
357 views

How do I know which force to use in moments calculation?

I'm working on some Statics problem, with the method of joints, etc and for all of them, we use sum of moments = 0. However, I'm very confused about which forces I should use to find the sum of ...
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1answer
164 views

Hanging a brick free over an edge by stacking them

National Geographics TV has a series called "None of the above". In one episode the presenter shows that by stacking 4 bricks (here shown as 'xxxxxxxx') you can have one of the bricks completely hang ...
2
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1answer
196 views

Relative strength of a dome [closed]

Is there a rough way to determine how the height of a dome affects the load that dome could support? For instance, assuming the bases of two domes are 24" in diameter, and one dome is 2" high while ...
2
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1answer
48 views

Sign of gravitational force

I'm reading Lanczos's The variational principles of mechanics, and on pp. 80-81 there is an example involving a system made up of $n$ rigid bars, freely jointed at their end points, and the two free ...
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0answers
708 views

Shape of a string/chain/cable/rope/wire?

The height of a string in a gravitational field in 2-dimensions is bounded by $h(x_0)=h(x_l)=0$ (nails in the wall) and also $\int_0^l ds= l$. ($h(0)=h(l)=0$, if you take $h$ as a function of arc ...
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1answer
160 views

Finding the Shape of a Hanging Massive Wire

This came from a physics wave book. I have a static, massive wire on the x-axis, with a y-displacement due to a force per unit length $F_y$. I start with the equation $F_y = ...
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1answer
309 views

Calculating stiffness of a beam of non-constant cross section

I am considering a paraboloid shape which is fixed at its base and is being compressed downwards. I am trying to find its stiffness so I can calculate how much it deforms. When I attempt to do this I ...
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2answers
476 views

Static equilibrium question [closed]

I was doing some static equilibrium problems and I came across this problem which should be easy to solve, but is posing quite a challenge. I want to point out that this is not homework, just plain ...
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0answers
141 views

Friction force problem for a 4 wheel drive Car [closed]

The car is a 4 wheel drive in equilibrium, the car doesn't touch the ground with the front wheel (A) but is in contact in B with the sidewalk (the sidewalk has a hight equal to $h$), the friction ...
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1answer
48 views

Optimal placement of support joist under shelf

Assume an ideal board, supported by two joists. Where should those two joists be optimally placed? Instinctively, I'd say at somewhat less than 25% and somewhat more than 75% of the extend of the ...
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2answers
136 views

Centre of mass and objects tipping [closed]

In this picture if the only parts of an object in contact with a surface are the lines AB and CD am I right in saying that the centre of mass has to be in the area enclosed by ABCD (as shown). I ...
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1answer
594 views

Mechanics question - ladder leaning against a wall

I am struggling with part a) of this question: Here is the solution: In part a) they prove that $F \leq \mu R$ is false for this system. So as $F$ is neither less than nor equal to $\mu R$ it ...
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4answers
3k views

Blocks stacked on an incline connected by rope around pulley

Two objects A and B, of masses 5 kg and 20 kg respectively, are connected by a massless string passing over a frictionless pulley at the top of an inclined plane, as shown in the figure. The ...
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1answer
2k views

A Bar Suspend by Two Wires - PHYS I HW [closed]

A nonuniform horizontal bar of mass $m$ is supported by two massless wires against gravity. The left wire makes an angle $ϕ_1$ with the horizontal, and the right wire makes an angle $ϕ_2$. The bar ...
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0answers
37 views

The magnitude of the resultant? [closed]

The two structural members, one of which is in tension and the other in compression, exert the indicated forces on joint O. Determine the magnitude R of the resultant R of the two forces and the angle ...
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2answers
730 views

Calculating axle load in cargo container (pics are included)

I'm current developing cargo loader software, but i have a little challenge with calculating load for each axle when a cargo is placed on container. I know that all axles will be affected (the nearest ...
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1answer
719 views

Given moment about a pin and a roller [closed]

sorry to ask, have not been a able to find a similar question to mine. For this problem, given moment $M_2$, distances $a$ and $b$ My reasoning is that we have two support reactions and points A and ...
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1answer
367 views

Using Moments to influence the thickness of beams in structure?

Are moments relevant to the thicknesses of beams in a structure (ie. the larger the moment the thicker the beam)?
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1answer
179 views

Moment around a point in a frame

Note: Both diagrams are 2d(they might look 3d because I drew them manually.) I have a prismatic frame that looks like this: I made a section on the half of the first pillar(the red line represents the ...
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2answers
724 views
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1answer
237 views

Moment of weight of leaning beam

Having trouble with a FBD moment. The problem is: How big can the force couple C (looks like a G in the pic) be in order for the disk to not spin? The disc has mass m and the beam also has mass ...
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1answer
201 views

Weird assumption in free body diagram problem

The assignment is to eventually calculate the forces on the BD beam of this picture: My issue is that on the solution sheet, the professor drew a free body diagram (FBD) for just the beams, with ...
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2answers
155 views

Friction acting on mass on string

Assume we have some stationary point mass that would slide, if not for some coefficient of friction, along a light, inextensible string, attached to two points at different heights. Considering ...
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1answer
1k views

Tension on pulleys Physics Question [closed]

Collar A is connected to a 50lb load on a frictionless horizontal rod. Determine magnitude of P to maintain equilibrium when x=4.5. Im confused on the concept of Tension I originally got the ...
4
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3answers
420 views

Moment of Inertia, why $r^2$and not $r$?

So my engineering mechanics book includes a brief discussion on area moments of inertia. Unfortunately, the ensuing chapter is predominately computational in nature. I don't have a thorough grasp of ...
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3answers
1k views

Formula for implementing a simulated weighing scale

Background: I'm on the pledge drive committee for a non-profit group, and there is an issue that is always contentious within this group; thankfully the group is amicable, although competitive, about ...
2
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1answer
100 views

Can all systems be put in equilibrium?

I'm in a first year statics course. We have spent the whole semester solving for forces and moments so that the system is in equilibrium. When we are given a system, we immediately begin solving for ...
2
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2answers
424 views

A man pulling himself up on a platform

Consider the following image: Is it possible that the man pulls himself up (suppose the weight of the platform is negligible), or just lift the right part of the platform up? How to analyse this ...
4
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1answer
708 views

Why don't couple forces violate Newton's First Law?

If you have some random object at rest and you apply a couple to it, the net force acting on it is zero. However because a moment acts on it, it starts to rotate. So you had an object at rest, a net ...
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1answer
648 views

Shear Flow corresponding to Eccentric Shear Force of a Closed-section Beam (Structural Analysis - Mechanics)

Been stumped with this question for way too long... its a beam with a thin-walled rectangular cross-section, and a shear force is acting at a distance from the shear center. I know my decomposition of ...
5
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1answer
173 views

Number of decays in a chain reaction

It is widely known that the probability of $n$ decays from one system to another $A \rightarrow B$ (e.g., electrons decaying from one atomic energy level to another or muons decaying into neutrinos ...
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1answer
1k views

Direction of tension?

If you draw the free body diagram of the frame above, what direction would the tension force acting on the frame be - to the right or down? Because the rope it horizontal at some points but vertical ...
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1answer
2k views

How to calculate the supporting force for a cantilever beam? [closed]

How do I find the supporting force $R_A$ and the moment $M_A$? Should I use the sum of moments or?
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2answers
2k views

Do objects rotate around the torque vector or its center?

If I have an sphere and I have a torque vector coming out of it at point A. Would the sphere rotate around its center or the axis of the torque vector?
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1answer
338 views

Why does moment equilibrium at one point of an object mean the moment is at equilibrium for the whole system?

In class my prof said that when showing a system is at equilibrium it suffices to show that the moment at one point is zero. Why? Why does showing the moment at a point is zero imply the moment of the ...