Tension in the block string

In summary, the blocks A and B are connected by a massless string and are subjected to forces Fa = 12N and Fb = 24N, respectively. The tension in the string is equal to the forces and remains constant throughout, regardless of the individual accelerations of the blocks.
  • #1
theunloved
43
1
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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  • #2
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.
 
  • #3
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 ?
 
  • #4
A single massless string can not have different tensions at different parts
 
  • #5
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.
 

Related to Tension in the block string

What is tension in a block string?

Tension in a block string refers to the force or pull exerted on the string by the weight of the block hanging from it. It is also influenced by other factors such as the angle of the string and the friction between the string and the block.

How is tension calculated in a block string?

Tension can be calculated using the formula T = mg, where T is the tension, m is the mass of the block, and g is the acceleration due to gravity. The angle of the string and the coefficient of friction can also be taken into account in the calculation.

What factors affect tension in a block string?

The factors that affect tension in a block string include the weight of the block, the angle of the string, the coefficient of friction between the string and the block, and any external forces acting on the string.

How does tension affect the motion of a block in a string?

Tension plays a crucial role in the motion of a block in a string. It is responsible for keeping the block suspended and determining the speed and direction of its motion. If the tension is too low, the block may fall or move in an unexpected direction.

Can tension in a block string be greater than the weight of the block?

Yes, tension in a block string can be greater than the weight of the block. This can happen if there are external forces acting on the string, or if the angle of the string is steep enough to increase the tension. However, the maximum tension that can be exerted on the string is limited by its breaking point.

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