Supporting a plank of wood with a mass at the centre

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Homework Help Overview

The discussion revolves around a scenario where two individuals are holding a plank of wood with a mass positioned at its center. As they walk backwards while extending their arms, the original poster questions why it becomes more challenging to support the plank in this configuration.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants explore the concept of moments and whether the individuals act as pivots. There is discussion about the forces involved and the implications of the plank's bending in a real-world scenario. Some participants question the clarity of the problem statement and whether the individuals maintain their grip at the ends of the plank.

Discussion Status

The conversation is ongoing, with participants clarifying their understanding of the problem and exploring different interpretations. Some have offered insights into the physical implications of the setup, while others are still seeking guidance on how to approach the question.

Contextual Notes

There is mention of potential misunderstandings regarding the problem's wording, and participants are reflecting on the accuracy of their notes and the teacher's intent. The discussion also touches on the difference between ideal and real-world scenarios concerning the plank's behavior.

Apothem
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Homework Statement


"Two people are holding a plank of wood at either end, with a mass located at the halfway point between them, they both walk backwards extending their arms, the mass still being halfway between them. The plank becomes harder to support, why is this?"

Homework Equations


Maybe the idea of moments?

The Attempt at a Solution


If it involves the use of moments do I deem the people are acting as pivots? As I haven't really given a "solution" could you perhaps point me in the right direction, so I can come to the answer?

Thanks.
 
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Did you draw a sketch with the relevant forces?

I see a possible real-life effect that could make it harder, but that is beyond the typical "find the forces" problems.
 
I assume that at first the two people are supporting the plank at some point not at the ends of the plank? In any case, it is not obvious to me that it will become harder to support the plank as they move towards the ends of the plank. Is that all the information you have? Or are they holding the ends of the plank at all times, and just walking back with their hands now extended?
 
I think the teacher was just trying to use an analogy to make it easier to understand. I am just in the process of creating images, which I will upload in a second.
 
7i8ExlR.png


It could well be possible I misunderstood the question the teacher asked, as we did have to write it down, if so I will ask next time I see him.
 
Doc Al said:
Or are they holding the ends of the plank at all times, and just walking back with their hands now extended?
Hmm, that would make sense. I don't see how the problem statement would lead to this interpretation, but then it is really getting harder.

As shown in post 5, the forces stay exactly the same with an ideal plank. A real plank would bend more in the second setup, which could it make harder to carry.
 
mfb said:
Hmm, that would make sense. I don't see how the problem statement would lead to this interpretation, but then it is really getting harder.

As shown in post 5, the forces stay exactly the same with an ideal plank. A real plank would bend more in the second setup, which could it make harder to carry.

Maybe it is that then, as I said I probably misheard what the teacher said when I wrote the problem down.
 
Doc Al said:
I assume that at first the two people are supporting the plank at some point not at the ends of the plank? In any case, it is not obvious to me that it will become harder to support the plank as they move towards the ends of the plank. Is that all the information you have? Or are they holding the ends of the plank at all times, and just walking back with their hands now extended?

Sorry I have just looked over my notes and realized that I wrote: "two people are holding the plank at either end they move further apart", so it must mean they are just walking back". I'll edit it on the first post now
 
Apothem said:
Sorry I have just looked over my notes and realized that I wrote: "two people are holding the plank at either end they move further apart", so it must mean they are just walking back". I'll edit it on the first post now
Good. Now the problem makes some sense.
 
  • #10
Doc Al said:
Good. Now the problem makes some sense.

Could you give me a hint of how to approach the question please?
 
  • #11
No need for help anymore I have figured it out! Thanks anyway.
 
  • #12
Apothem said:
No need for help anymore I have figured it out! Thanks anyway.
Good. I think you gave yourself your own hint: Moments.
 

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