# Doubt about solution -- Two masses connected by a rod moving on a surface

• String theory guy
In summary: Static friction would not be enough to keep them in contact.It says they're connected, so I would take that as meaning they are somehow secured together.
String theory guy
Homework Statement
The statement is below.
Relevant Equations
Newton's Second Law
The doubt is about this question.

Which the answer is

They say that all the forces are pulling forces? How is this the case?

How would this setup even work? I don't think block 2 could pull the rod.

String theory guy said:
They say that all the forces are pulling forces? How is this the case?
Can you find one that isn't?

String theory guy
Yes I can @haruspex :
F1, rod
F2, rod

String theory guy said:
Yes I can @haruspex :
F1, rod
F2, rod
F1,rod is the force m1 exerts on the rod. That force pulls the rod to the left.

String theory guy
haruspex said:
F1,rod is the force m1 exerts on the rod. That force pulls the rod to the left.
I thought it was the opposite way round. How did you derive that @haruspex ?

String theory guy said:
I thought it was the opposite way round. How did you derive that @haruspex ?
Do you mean, how do I know that F1,rod is the force m1 exerts on the rod, not the force the rod exerts on m1? Because clearly everything does move to the right, and the only way m1 is going to move to the right is if the force the rod exerts on m1 is to the right. So that must be Frod,1.
But the question ought to have made the notation clear.

String theory guy
haruspex said:
Do you mean, how do I know that F1,rod is the force m1 exerts on the rod, not the force the rod exerts on m1? Because clearly everything does move to the right, and the only way m1 is going to move to the right is if the force the rod exerts on m1 is to the right. So that must be Frod,1.
But the question ought to have made the notation clear.
Yea that is my doubt I think @haruspex - how dose everything in the system move to the right? Is there some glue or something between the block and masses? That is the only way I can see mass 1 moving to the right being in contact with the rod that is moving to the right.

I don't know, but the force of static friction should not be that great allowing the rod to pull mass 1.

String theory guy said:
Is there some glue or something between the block and masses?
It says they're connected, so I would take that as meaning they are somehow secured together.

String theory guy

## What is the setup of the problem?

The problem involves two masses connected by a rod, moving on a surface. The masses have different masses and are connected by a rigid rod. The surface on which they are moving is assumed to be frictionless.

## What is the equation used to solve this problem?

The equation used to solve this problem is the Newton's Second Law of Motion, which states that the net force acting on an object is equal to its mass times its acceleration. In this case, the net force acting on the masses is the tension in the rod, and the acceleration is the same for both masses since they are connected by the rod.

## What are the assumptions made in this problem?

The assumptions made in this problem are that the surface is frictionless, the rod is rigid, and there are no external forces acting on the system. Additionally, the masses are assumed to be point masses and there is no air resistance.

## How do you find the acceleration of the masses?

To find the acceleration of the masses, we can use the equation derived from Newton's Second Law of Motion: a = (m1-m2)g / (m1+m2). This equation takes into account the masses of the two objects and the force of gravity acting on them.

## What is the significance of this problem?

This problem is commonly used in physics to demonstrate the concept of tension and the application of Newton's Second Law of Motion. It also helps to understand the dynamics of a system with multiple masses connected by a rigid rod.

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