Find the accelerations of all three blocks and the tension in the rope

In summary, the conversation discusses solving a problem using Newton's laws and a system of equations. The fourth equation is a constraint equation and there is a possibility of a sign error. The individual plans to learn LaTex after exams and there is a discussion about the consistency of the equations. It is determined that the system is solvable with 4 equations and 4 unknowns.
  • #1
rashida564
220
6
Homework Statement
In the system shown above m1 > m2 . The pulleys are massless and frictionless, and the
rope joining the blocks has no mass. The coefficient of static friction between the blocks
and the tables is greater than the coefficient of kinetic friction: µs > µk . The downward
acceleration of gravity is g .
Now consider the case where, when released from rest, all three blocks
begin to move. Find the accelerations of all three blocks and the tension in
the rope.
Relevant Equations
F=ma
I am thinking about solving it this way.
The first three equation is from Newton law.
Then the forth one is the constrain equation, after that I simplified the first three equations, and I am thinking about plugging them into the forth equation and solve for T after that I get the value of each acceleration, but I have 10% scared that I am having sign wrong in one of them.
Sorry about writing the equation as picture I want to improve my writing, but going to learn LaTex after exams.
 

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  • #2
I believe in order to be consistent with your first 3 equations, the fourth equation should read ##a_{1} + a_{2} = 2a_{3}##, since all of the accelerations are taken to be positive. Either that or reverse the signs of the first two Newton II relations, to be consistent with the directions of ##x_{1}## and ##x_{2}## on your diagrams. It doesn't matter which you choose.

Then, the system has 4 equations and 4 unknowns so it should be possible to solve.
 
  • #3
Thanks mate, now I see my mistake.
 

1. How do you find the accelerations of the three blocks?

To find the accelerations of the three blocks, we can use Newton's Second Law of Motion, which states that the sum of all the forces acting on an object is equal to its mass multiplied by its acceleration. By analyzing the forces acting on each block and setting up equations of motion, we can solve for the accelerations.

2. What information do you need to find the accelerations and tension?

In order to find the accelerations and tension in the rope, we need to know the masses of all three blocks, the forces acting on each block (including the tension in the rope), and the coefficients of friction between the blocks and the surface they are on. We also need to know the direction of motion for each block.

3. How do you determine the tension in the rope?

To determine the tension in the rope, we can apply Newton's Second Law of Motion to the block that is attached to the rope. By setting up an equation with all the forces acting on the block (including the tension), we can solve for the tension in the rope.

4. What factors affect the accelerations and tension in this system?

The mass of each block, the forces acting on each block (such as friction and external forces), and the direction of motion for each block can all affect the accelerations and tension in the system. Additionally, the coefficient of friction between the blocks and the surface they are on can also impact the accelerations and tension.

5. Can the accelerations of the blocks be negative?

Yes, the accelerations of the blocks can be negative if they are slowing down or moving in the opposite direction of the positive direction defined in the problem. It is important to consider the direction of motion when solving for the accelerations in this system.

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