Supporting a plank of wood with a mass at the centre

[Apothem]

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.

 

[mfb]

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.

 

[Doc Al]

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?

 

[Apothem]

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.

 

[Apothem]

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.

 

[mfb]

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.

 

[Apothem]

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.

 

[Apothem]

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

 

[Doc Al]

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.

 

[Apothem]

Good. Now the problem makes some sense.

Could you give me a hint of how to approach the question please?

 

[Apothem]

No need for help anymore I have figured it out! Thanks anyway.

 

[Doc Al]

No need for help anymore I have figured it out! Thanks anyway.

Good. I think you gave yourself your own hint: Moments.