A massless, frictionless pulley is suspended from a rigid rod

In summary, the problem involves a massless, frictionless pulley with two masses, m (50 kg) and M (60 kg), suspended on either side by light, inextendable cords. The force diagrams show an upward tension force and a downward gravity force for each mass. The acceleration of the masses can be determined using the equation Mg - mg = (m + M)a. Depending on how the coordinate system is defined, m may have a positive acceleration while M has a negative acceleration.
  • #1
Soaring Crane
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A massless, frictionless pulley is suspended from a rigid rod. Two masses, m (50 kg) and M (60 kg), are suspended on either side of the pulley, respectively, by a light, inextendable cord. Determine the accelerations of the masses.

I drew the force diagrams of both; there is an upward tension force and a downward gravity force in each. Mg - mg = (m + M)a. Now acceleration of block m is (M - m)g/(M + m) upward and block M's acceleration is the same but downward. So does m have a positive acceleration while M has a negative acceleration?

Thanks.
 
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  • #2
Could be either, it depends upon how you define your coordinate system. Is postive up or down?
 
  • #3
I guess I define positive as going up on the coordinate sys. In the problem, m is pulled up while M goes down.
 

1. What is a massless, frictionless pulley?

A massless, frictionless pulley is a hypothetical device used in physics problems to simplify calculations. It is assumed to have no mass and no friction, allowing for the tension in the rope to remain constant throughout the system.

2. How does a massless, frictionless pulley work?

A massless, frictionless pulley works by redirecting the force applied to the rope. When a force is applied to one side of the rope, the tension in the rope causes an equal force to be applied to the other side, resulting in a change in direction of the force.

3. How is a massless, frictionless pulley suspended from a rigid rod?

A massless, frictionless pulley is typically suspended from a rigid rod by a frictionless bearing. This allows the pulley to rotate freely without any resistance or friction.

4. What are the advantages of using a massless, frictionless pulley in physics problems?

The main advantage of using a massless, frictionless pulley in physics problems is that it simplifies the calculations and allows for easier analysis of the forces at play. It also eliminates the need to consider the weight and friction of the pulley itself.

5. Are massless, frictionless pulleys physically possible?

No, massless, frictionless pulleys are purely hypothetical devices used for theoretical calculations. In reality, all pulleys have some mass and friction, although these factors may be negligible depending on the specific situation.

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