# Why is tension present in the rope?

1. May 7, 2015

### Churchill Tech

These is my problem

Assuming the surface on which A rests is frictionless and there is no drag on either of the bodies as they move at common acceleration.

Correct me if I’m wrong, I think the bodies should have a common acceleration since they’re connected

Why does F? exist??, I know that F? is exerted on the body B such that the net force on B downwards is less than mg but what is causing this force?, Looks to me like this force is a pull on the string by A but I don’t think there is any force acting to the left of body A besides friction and drag which I have assumed to be non-existent.

I would be grateful on getting well explained answer...Help me guys.

2. May 7, 2015

### Staff: Mentor

Even if there is no force pulling to the left on A, the force F is still necessary to accelerate A. (A is not in equilibrium).

Chet

3. May 7, 2015

### Staff: Mentor

Yes. Both A and B exert forces on the string equal to F.

Why would you need a force to the left of A?

4. May 7, 2015

### Staff: Mentor

Inertia.

Which, by the way, you need to consider for both objects, not just A.

5. May 7, 2015

### sophiecentaur

Perhaps the easiest way to approach this is to think in terms of the Force being mg and that this force acts on the combined mass m+m2.

6. May 7, 2015

### Staff: Mentor

But that won't explain the tension in the string.

7. May 7, 2015

### sophiecentaur

The tension would be there because the mass m2 is being accelerated at the rate that was just calculated. F = mA again

8. May 8, 2015

### Staff: Mentor

Suppose F is the tension in the string. Have you drawn free body diagrams on the two masses? Please write down the force balance equation you obtained from these free body diagrams for each of the masses.

Chet