Is the Tension in the String Equal for Both Blocks?

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Homework Help Overview

The discussion revolves around the tension in a string connecting two blocks of different masses, specifically a 4.0 kg block A and a 6.0 kg block B. Forces are applied to each block, with Fa = 12N acting on block A and Fb = 24N acting on block B. Participants are exploring the implications of these forces on the tension in the string.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to understand why the tension in the string (Ta and Tb) should be equal despite the different applied forces on each block. They question the implications of unequal tensions on the system's behavior.
  • Some participants suggest that since the string is massless, the tension must be the same throughout, prompting further exploration of the forces acting on each block and their directions.
  • Others raise the point that if one force is greater than the other, it could lead to different accelerations, which complicates the assumption of equal tension.

Discussion Status

Participants are actively engaging with the problem, questioning the assumptions about tension and exploring the relationships between the forces and accelerations of the blocks. There is a recognition of the need to clarify the equations governing the system, but no consensus has been reached regarding the implications of the different forces on tension.

Contextual Notes

There are discussions about the direction of the forces and the implications of having different applied forces on the blocks. The original poster expresses confusion about the relationship between the forces and the resulting tension, indicating a need for further clarification on these concepts.

theunloved
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4.0 kg block A and 6.0kg block B are connected by a string of negligible mass. Force a Fa = 12N acts on block A; force B Fb = 24N acts on block B. What is the tension in the string.

I was able to draw FBD and lists all the forces acting on A and B, but what I don't understand is the tension T acting on A and B.
A:
Fa - Ta = m1 A

B:
Fb - Tb = m2 A

In my understanding, Ta and Tb shouldn't be equal, since we have Fa and Fb exerts on each object and they have different value. What if Ta > Tb, then the cord between A and B should come loose, therefore we'd not have tension at all. But if we don't have have Ta = Tb, then there's no way we can solve the problem...
So my question is: Is it really Ta = Tb and why ?
 
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The tension is equal, it's just one string after all. What directions are the forces acting? If they are opposite from one another, your equations are close, but one of the applied forces should be negative, with tension adding, while one of the applied forces should be positive, with tension subtracting.

Knowing mass, and knowing the acceleration of the system is equal, and knowing tension is equal, you can solve for tension. You're nearly there, correct your equations, solve both for A, then set them equal to one another, and solve for T. At least that's how I remember doing these.
 
1MileCrash said:
The tension is equal, it's just one string after all. What directions are the forces acting? If they are opposite from one another, your equations are close, but one of the applied forces should be negative, with tension adding, while one of the applied forces should be positive, with tension subtracting.

Knowing mass, and knowing the acceleration of the system is equal, and knowing tension is equal, you can solve for tension. You're nearly there, correct your equations, solve both for A, then set them equal to one another, and solve for T. At least that's how I remember doing these.

Oh, yeah,
Both Fa and Fb have the same direction, going from left to right.
So it should be
Tension in the string
4.0 kg block A and 6.0kg block B are connected by a string of negligible mass. Force a Fa = 12N acts on block A; force B Fb = 24N acts on block B. What is the tension in the string.

I was able to draw FBD and lists all the forces acting on A and B, but what I don't understand is the tension T acting on A and B.

A:
Fa + Ta = m1 A

B:
Fb - Tb = m2 A

I know that its from one string, the tensions should be equal, but, here, we have Fa and Fb. Don't we on the force acting on A and B ? they are different, and they are the forces that make A and B moving. So, if you have Fa > Fb, A will be moving faster than B, and since it's moving faster, it'll catch up with B in a certain time, if that's the case, shouldn't the tensions be different ?
 
A single massless string can not have different tensions at different parts
 
theunloved said:
Oh, yeah,
Both Fa and Fb have the same direction, going from left to right.
So it should be
Tension in the string
4.0 kg block A and 6.0kg block B are connected by a string of negligible mass. Force a Fa = 12N acts on block A; force B Fb = 24N acts on block B. What is the tension in the string.

I was able to draw FBD and lists all the forces acting on A and B, but what I don't understand is the tension T acting on A and B.

A:
Fa + Ta = m1 A

B:
Fb - Tb = m2 A

I know that its from one string, the tensions should be equal, but, here, we have Fa and Fb. Don't we on the force acting on A and B ? they are different, and they are the forces that make A and B moving. So, if you have Fa > Fb, A will be moving faster than B, and since it's moving faster, it'll catch up with B in a certain time, if that's the case, shouldn't the tensions be different ?
If Fa > Fb, solve for T. Strings cannot take negative tensions, they go slack. The blocks accelerate independently from each other. What would be the value of T for that case? As noted,the tension in a massless string must be the same throughout.
 

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