# Tagged Questions

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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### Why can contact force be ignored here?

I was discussing the first part of this question with a friend, and he told me that while taking moments about $A$ and $B$, we can ignore the reaction force at C. Indeed this is correct, because ...
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### Statics with ladder and wall [closed]

A uniform ladder of mass m and length L rests against the wall. The coefficients of static friction between the floor and the ladder and between the wall and the ladder are equal to each other (μ). ...
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### When a force applies to a rigid body at point, then does every part of the body experience the same kind of force?

Suppose that a rigid body is static under the action of several forces that are applied at different part of the body. Then is it true that if one divides the body into small pieces, then each piece ...
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### Tension of string attached to ball on inclined plane [closed]

A sphere of weight 50N and radius 4cm is held by a string of length 8 cm against a smooth wall inclined at an angle of $70^{\circ}$. Find the tension in the string and the force between the ball and ...
339 views

### What force $\vec{F_{1}}$ is needed to balance the beam in the diagram below? [closed]

What force $\vec{F_{1}}$ is needed to balance the beam in the diagram below? I know that $\sum \vec{F}$ must equal zero. I also know that since the unknown force is farther from the pivot, it ...
314 views

### How does the net torque have to be 0 at all points for static equilibrium? [duplicate]

I know that for a mass to be in static equilibrium two things have to be satisfied: $\sum F=0$ and $\sum T=0$, where $T$ represents torque. However, I am not sure how the latter can apply in a ...
348 views

### Tension on strings holding a weight [closed]

It's a 100% standard problem in any basic physics course, and I cannot solve it. Here's the scenario: What is the tension in the strings (T1 and T2)? My thoughts were (cos/sin rewritten as cos(60&...
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### Find center of mass and moment applied on beam structure [closed]

I have a simple physics problem to solve but it is giving me a slightly difficult time to figure out. The problem: I have a beam structure with same cross section. It consists of three beam. First ...
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### Parallel axis theorem

For this question we are working in 2-D space. Let's say that we have an arbitrary body. I know the inertia with respect to a perpendicular axis (to the body, that is) that passes through a point (A). ...
272 views

### Finding minimum force to hold a particle in equilibrium [closed]

A particle of mass $m$ is suspended from a point A on a vertical wall by means of a light inextensible string of length $b$. Find the magnitude and direction of the minumum force $\boldsymbol P$ that ...
593 views

### Prevent a box from tipping over: height of CG?

I'm on a problem that can be simplified in the following way: A box is placed on a horizontal plane, and is pinned to the ground on one side only such that it can tip over that side. Given a ...
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### The principles of statics without force

I'm a student of civil engineering and now my course is covering the basics of statics, such as the equations of equilibrium, etc. Trying to get a better basis on the subject, I started to search on ...
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### Forces exerted on legs of a table

This is actually for a computer science homework problem, but I haven't studied any physics in five years so I'm having a bit of trouble. I'm given a table of three legs with their coordinates and I ...
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### Dropping vertices of an overdetermined statics system graph

In statics, the problem of determining the tensions of K cables that connect a structure made of N points and keep all points in static equilibrium implies $ND$ systems of equations, where $D$ is the ...
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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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### 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, ...
164 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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### 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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### 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 ...
5k 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. So ...
510 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 ...
2k 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 ...
891 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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### 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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### 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 ...
1k 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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### 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 ...
638 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: i....
968 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 ...
239 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 ...
363 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 ...
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### 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 ...
983 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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### 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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### 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 ...
1k views

### How do I find the tension in the cable from this problem? [closed]

I am trying to find the tension of the cable but I don't know what to do.
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### 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 m. ...