Massless beam held against a wall

In summary: I'm not entirely sure what you are asking. Let's try and clarify: what exactly is the "massless string"? Is it just a string? If so, what is the mass of the string? How is the massless beam being held against the wall? Is the beam hinged or frictionless?
  • #1
bboytymee
2
0

Homework Statement


Just took my finals and there was one problem that bugged me, I have done these types of problems multiple times and understand it well but this particular problem seems like there isn't enough information.

There is a massless beam being held against a wall by a massless string. A 2000N mass is attached to the end of the beam. The beam is L meters in lenght. The distance from the string on the wall to the end of the beam touching the wall is L. The beam is θ degrees above the horizontal.
a) Find the tension in the string
b) Find the angle θ
c) Find the horizontal and vertical force being exerted on the massless beam by the wall.

Basically the only value you have is 2000N, and you know that the distance of the beam and the distance of the wall is equal, and therefore it forms an isosceles triangle.

I couldn't find a picture of the problem but the set up is similar to this
http://s3.amazonaws.com/answer-board-image/cddfc98e-12fc-48cb-9ef4-c645d675f561.jpeg
except the bar is tilted at angle θ, the length of the bar is L.

Homework Equations


τ=Flcosθ

The Attempt at a Solution



I understand the equations and isolation of systems completely, the only thing that is restricting me from solving the problem is finding the value of θ so I was wondering if anyone who is really good at trig could help.
 
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  • #2
There is clearly not enough information here. Are you sure you have this verbatim?
 
  • #3
I thought so, yes this is verbatim. All of my peers in class wern't able to solve it either so I'm sure there isn't enough information. Just wanted to see if someone with higher knowledge thought the same.
 
  • #4
It doesn't seem completely unsolveable. I've done similar problems. Let's see what equations we can set up... forces in y direction (equal to 0), forces in x direction (also 0), balancing of torques (also 0) and maybe some trig equations: addition of angles and the law of cosines *could* possibly help.
 
  • #5
One thing that intrigues me is this phrase: "being held against a wall by a massless string". What exactly does that mean? Only one end of the beam touches the wall. It almost suggests it's just resting against the wall rather than hinged, but there would have to be some friction or the beam would slip (unless theta=0), so it might as well be hinged. Maybe it is supposed to be frictionless and hingeless, in which case it is easy to solve.
 

1. What is a massless beam held against a wall?

A massless beam held against a wall is a hypothetical scenario in which a beam with no mass is placed horizontally against a vertical wall. This is often used in physics problems to simplify calculations and focus on the effects of forces.

2. How can a beam have no mass?

In physics, the term "massless" does not necessarily mean literally having no mass. It is used to describe objects that have very little mass in comparison to other objects in the scenario. In the case of a massless beam, it means that the mass of the beam can be ignored in calculations because it is much smaller than the other masses in the system.

3. What forces act on a massless beam held against a wall?

In this scenario, there are two main forces acting on the beam: the normal force from the wall pushing against the beam and the weight of any objects placed on the beam. The normal force is equal in magnitude and opposite in direction to the weight of the objects, and these forces keep the beam in equilibrium.

4. Can a massless beam actually exist?

No, a massless beam cannot exist in reality. All objects have some mass, no matter how small, and a beam must have some mass in order to support any weight placed on it. The concept of a massless beam is simply a way to simplify calculations in certain physics problems.

5. What are the limitations of using a massless beam in calculations?

The main limitation of using a massless beam in calculations is that it does not accurately represent real-world scenarios. In reality, beams have mass and this can affect their strength and stability. Therefore, using a massless beam in calculations may lead to inaccuracies in the results. It is important to keep in mind the limitations and assumptions when using this concept in problem-solving.

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