How do you calculate tension and frictional forces in a system of moving bodies?

In summary, the conversation discusses a physics problem involving two masses connected by a cord and being pulled by an applied force. The question asks for the tension in the cord and the frictional force on each block. Different methods are suggested for solving the problem, including identifying all forces and applying Newton's 2nd law. The conversation also clarifies the directions of the tension and force on the two blocks.
  • #1
undertow2005
i'm working without my textbook and going by the some solutions that i have so i need some help

1) Two masses, m1 and m2, joined with a cord are dragged along the horizontal plane surface. the applied force is F=20N, mass m1=m2=3kg, and the acceleration is 0.50 m/s. what is the tension, T, in the connecting cord if the frictional forces on the two blocks blocks are equal? How large is the frictional force, F, on each block?
diagram:
| m1 |-----| m2|------>F
 
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  • #2
can you explain what you have done to try and solve this?
 
  • #3
i've solved simpled problems--problems with only one body moving. so i tried to apply those principles here:

for tension:
T=3kg*.50
i know know that is wrong since there is a frictional force. i just don't know how to compute it since the coefficient of friction is not given
so, there it is. i didnt get very far into it.
 
  • #4
Attack the problem step by step. Start, as always, by identifying all the forces acting on each of the masses. Draw a picture with those forces labeled. (All we care about are the horizontal forces.)

Once you've done that, there are several ways to proceed. Here's one way. Treat each mass separately and apply Newton's 2nd law. You'll get an equation for each mass. Combine them and you can solve for the tension in the cord and the fricitional force. Give it a shot.
 
  • #5
i did give it a shot, please I'm totally lost here, my Final that i must Ace is tomorrow. please work this problem out for me, somebody
 
  • #6
What forces are the front block subject to?
Clearly, the applied force F, a tensile force T, and a frictional force f.
Obviously, both the tensile force and the frictional force works in opposite direction than F, so we have for particle 2:
[tex]F-T-f=ma[/tex]
For the rear block, the tensile force has the same magnitude T, but works in the opposite direction.
Hence, we have:
[tex]T-f=ma[/tex]
You have only 2 unknowns here, T and f, and 2 equations..
 
  • #7
from the equations i know how get get T and f. i have another question, how do you know T is opposite the force. i acutally thought T was going the same direction as the force for the box in the front. or is the tension always opposite the force. also, for the box in the rear, why did you leave out F out of the equation and not write F-T-f=m*a. i don't understand because the force is also acting on this box.
 
  • #8
undertow2005 said:
i have another question, how do you know T is opposite the force. i acutally thought T was going the same direction as the force for the box in the front. or is the tension always opposite the force.
The tension in the cord exerts a pull (T) at both ends of the cord. According to your diagram, the cord pulls m1 to the right and m2 to the left.
also, for the box in the rear, why did you leave out F out of the equation and not write F-T-f=m*a. i don't understand because the force is also acting on this box.
The force F is only applied to mass m2; it does not touch m1. It will, of course, affect the tension in the connecting cord--but that's a separate force.
 

1. What is a "System of moving bodies"?

A system of moving bodies refers to a group of objects or particles that are constantly changing their position or motion in relation to each other. This can include planets in a solar system, molecules in a chemical reaction, or even people in a crowded room.

2. How is a system of moving bodies studied?

A system of moving bodies is studied using the principles of physics, specifically mechanics and dynamics. This involves analyzing the forces acting on the bodies, their positions and velocities, and predicting their future movements using mathematical equations and models.

3. What factors affect the behavior of a system of moving bodies?

The behavior of a system of moving bodies can be affected by various factors such as external forces, the mass and velocity of the bodies, and the presence of forces like friction or gravity. The initial conditions and interactions between the bodies also play a significant role in determining their behavior.

4. Can a system of moving bodies be accurately predicted?

While the behavior of a system of moving bodies can be predicted using mathematical models, it is not always accurate due to the complexity of the system. Factors such as unpredictable external forces or errors in measurements can affect the accuracy of predictions.

5. What real-life applications involve the study of systems of moving bodies?

The study of systems of moving bodies has many real-life applications, including predicting the trajectory of space objects, understanding the behavior of fluids in pipelines, and analyzing the movements of animals and humans. It is also important in engineering and design, as it helps in predicting the behavior and stability of structures and machines.

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