Rope, tension and Newtons third law

[DakE_FeatH]

This is more of a conceptual question, meant to help us understand how tension forces work.

Homework Statement

Assume that segment R exerts a force of magnitude T on segment L. What is the magnitude F_RL of the force exerted on segment R by segment L?
Give your answer in terms of T and other constants such as g.

Homework Equations

Fnet = ma

The Attempt at a Solution

Fnet = F_{R on L} + F_{L on R} = 0 (I assume it's 0)

I also know that Fnet = ma, but I don't know if I should use any mass, since it's a rope, and in first year undergraduate class, I understood that ropes are massless.

The question says in terms of g and I know that F_G=m*g (g = -9.81)

I don't know how to indroduce the g in the equations.

 

[Doc Al]

Consider Newton's 3rd law. (It's way easier than you think.)

 

[DakE_FeatH]

Ok, Newtons third law states that "every force occurs as one member of an action/reaction pair of forces". So the two objects have forces acting on them of the same magnitude but opposite directions.

I think I understand how the tension forces work horizontally, but I have no idea how to add the g in there. Is there also a normal force that is equal and opposite to g? If so, how? It's in the air so I don't understand where that would come from :(

 

[tiny-tim]

Welcome to PF!

Ok, Newtons third law states that "every force occurs as one member of an action/reaction pair of forces". So the two objects have forces acting on them of the same magnitude but opposite directions.

I think I understand how the tension forces work horizontally, but I have no idea how to add the g in there. Is there also a normal force that is equal and opposite to g? If so, how? It's in the air so I don't understand where that would come from :(

Hi DakE_FeatH! Welcome to PF!

What makes you think g is involved?

 

[DakE_FeatH]

What makes you think g is involved?

They say in the problem to give my answer in terms of T and "constants such as g"

So I can't just use Fnet = FR on L + FL on R = 0

 

[Doc Al]

They say in the problem to give my answer in terms of T and "constants such as g"

I think you are overly constraining yourself. I'm sure they meant: "... in terms of T and constants such as g if you need them".

If A exerts a force on B, then B exerts an equal and opposite force on A. That's Newton's 3rd law. Case closed.

 

[DakE_FeatH]

Ok I got it, it was |-T|, they just put in the g to mess me up. Thank you guys!