I really don't understand what I'm even being asked

[1MileCrash]

Homework Statement

Two skaters, one mass 65kg and one mass 40kg, stand on an ice rink holding a pole of length 10m and negligible mass. Starting from ends of the pole, the skaters pull themselves along the pole until they meet. How far does the 40kg skater move?

Homework Equations

The Attempt at a Solution

I don't even know what aspect of physics this is supposed to be about.

EDIT:

I looked at the solution and it says both skaters end up at the center of mass of the system. With that, the problem is trivial.

But to better my understanding, why do both skaters end up at the COM?

 

[Villyer]

My guess is that this is a conservation of momentum problem.

 

[1MileCrash]

Both skaters end up at the COM, but why?

 

[SammyS]

What is the net force exerted on the system?

 

[1MileCrash]

What is the net force exerted on the system?

ON the system, 0.

 

[DaveC426913]

ON the system, 0.

So, if no net external force is applied to a system, what happens (or doesn't happen) to its CoM?

 

[DaveC426913]

I looked at the solution and it says both skaters end up at the center of mass of the system. With that, the problem is trivial.

So what is the answer?

 

[1MileCrash]

So, if no net external force is applied to a system, what happens (or doesn't happen) to its CoM?

Then the COM cannot change.

But why is it that when they pull, they end up at the COM?

So what is the answer?

65(10)/105 = 6.2, taking the 40kg "puller" as origin, com is 6.2 meters from it.

 

[SammyS]

If they are very close together, then where is the COM relative to them?

 

[DaveC426913]

Then the COM cannot change.

But why is it that when they pull, they end up at the COM?

Where else would they end up?

Whether 10m apart or 0m apart, if the CoM has not moved, how could they be anywhere else?

 

[1MileCrash]

Where else would they end up?

Whether 10m apart or 0m apart, if the CoM has not moved, how could they be anywhere else?

Well, I don't know, that's what I'm asking. It only makes sense in my head if we assume that both pullers pull with the exact same force, which seems like an absurd assumption.

 

[SammyS]

But eventually they come together, correct?

 

[DaveC426913]

Well, I don't know, that's what I'm asking. It only makes sense in my head if we assume that both pullers pull with the exact same force, which seems like an absurd assumption.

What if they used completely different forces? What if the 65kg puller did all the pulling and the 40kg puller just hung on? Would that change anything?

Remember, they're on ice. No friction. Newton's First Law applies here.

 

[1MileCrash]

What if they used completely different forces? What if the 65kg puller did all the pulling and the 40kg puller just hung on? Would that change anything?

Wouldn't the center of mass move down the pole in that case?

Or... is it correct to say that the center of mass would move "down the pole" but the center of mass oriented in space, in the room, of the skater/pole system would stay the same? IE if I marked the center of mass on the ice underneath the pole. As the pole moves, the center of mass would still stay above that mark on the ice?

 

[DaveC426913]

Wouldn't the center of mass move down the pole in that case?

Or... is it correct to say that the center of mass would move "down the pole" but the center of mass oriented in space, in the room, of the skater/pole system would stay the same? IE if I marked the center of mass on the ice underneath the pole. As the pole moves, the center of mass would still stay above that mark on the ice?

Yes. The pole is massless. It is not a useful/meaningful reference point. If one person tugged on it and the other didn't the pole would move relative to the CoM. It's the CoM that acts as the meaningful reference point. And yes, it would remain over the pole.