Solve Tension in Three Blocks of Mass: m1, m2, m3

In summary, the conversation pertains to a physics question involving three blocks with different masses connected by strings over two pulleys. The question asks for the magnitude of the tension in the strings connected to blocks m1 and m3. The person found the acceleration to be 2.31m/s^2 and needed help with finding the net force. After being advised to make a Free Body Diagram, they were able to solve the problem and determine that T1 is equal to the sum of the force of gravity and the force being pulled up, while T3 is equal to the force of gravity subtracted by the acceleration.
  • #1
Northstar
7
0
I have a couple questions that I can't figure out regarding the following question. The picture pertains to the question.

http://img81.imageshack.us/img81/8229/physnd4.jpg

Three blocks of mass m1 = 4 kg, m2 = 5 kg and m3 = 8 kg are connected by strings which pass over two ideal pulleys as shown in the figure below.

What is T1, the magnitude of the tension in the string that is connected to the block of mass m1?

and

What is T3, the magnitude of the tension in the string that is connected to the block of mass m3?

I found acceleration to be 2.31m/s^2 (and it was correct). I know Fnet = ma, but for whatever reason I am setting something up wrong for Fnet. I thought Fnet would be the force of gravity acting on the block + the force being pulled up (in the case of m1) or the block going downward (as in m3).

Any help would be appreciated.
 
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  • #2
Try making a Free Body Diagram for the block in the middle. That will really help.
 
  • #3
Ok, I figured it out, thanks. Basically for T1 what I was doing wrong in the equation T = m (g-a) was taking 9.81-2.31 instead of adding them together. Then I was able to figure out that T3 was 8 (9.81-2.31).
 

1. How do you calculate the tension in three blocks of mass?

The tension in a system of three blocks can be calculated by using Newton's second law, which states that the net force acting on an object is equal to its mass multiplied by its acceleration. In this case, the net force is equal to the tension applied to the blocks, and the acceleration is the same for all three blocks. Therefore, the tension can be calculated by dividing the total mass of the system by the acceleration.

2. What is the formula for solving tension in three blocks of mass?

The formula for solving tension in a system of three blocks is T = (m1 + m2 + m3) * a, where T is the tension, m1, m2, and m3 are the masses of the blocks, and a is the acceleration of the system.

3. How does the mass of the blocks affect the tension in the system?

The mass of the blocks directly affects the tension in the system. The larger the mass of the blocks, the greater the tension required to accelerate them at a given rate. This is because the net force acting on the blocks increases with their mass, according to Newton's second law.

4. Can the tension in the system ever be less than the weight of the blocks?

No, the tension in the system will always be equal to or greater than the weight of the blocks. This is because the weight of the blocks is equal to the force of gravity acting on them, and the tension in the system must be at least equal to this force in order to prevent the blocks from falling.

5. What other factors can affect the tension in a system of three blocks?

In addition to the mass of the blocks, the tension in a system can also be affected by the angle at which the blocks are suspended, the friction between the blocks and the surface they are resting on, and any external forces acting on the blocks. These factors can impact the acceleration of the system and therefore affect the tension.

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