Work-Energy: Force Acting Through 1.2pi Despite 0.6pi Move

  • Thread starter Thread starter eurekameh
  • Start date Start date
  • Tags Tags
    Work-energy
AI Thread Summary
The discussion centers on the relationship between force, distance, and energy in a system involving a disk and an unwinding cord. It highlights confusion regarding why the force acts through a distance of 1.2pi while the disk's center only moves 0.6pi. The unwinding cord increases in length, necessitating that the force's application point moves further than the disk itself. Additionally, the force generates a moment about the center of mass, which should contribute to the total kinetic energy of the disk, encompassing both translational and rotational components. The conversation concludes by affirming that the solution to the problem addresses both forms of kinetic energy.
eurekameh
Messages
209
Reaction score
0
2ls6ziu.png

I don't understand why the force is acting through a distance of 1.2pi, even though the center of the disk clearly moves a distance of 0.6pi.
 
Physics news on Phys.org
The cord is unwinding. So the length of cord between where it meets the disk and whatever it is that's pulling on the cord will grow longer. Clearly whatever is applying the force to the free end of the cord has to mover further than the disk's center.
 
Isn't the force also causing a moment about the center of mass? Shouldn't this contribute to the work done?
 
eurekameh said:
Isn't the force also causing a moment about the center of mass? Shouldn't this contribute to the work done?

Doing work results in a change in energy, in this case a change in the energy of motion. Can you identify where the energy of motion is going to end up in this case?
 
Translational and rotational kinetic energy. The force moves through a distance of 1.2pi. But it is also causing a moment through an angle of 2pi. Shouldn't this moment through an angle also be contributing to the total kinetic energy (translational and rotational) of the disk?
 
eurekameh said:
Translational and rotational kinetic energy. The force moves through a distance of 1.2pi. But it is also causing a moment through an angle of 2pi. Shouldn't this moment through an angle also be contributing to the total kinetic energy (translational and rotational) of the disk?

You've identified translational and rotational kinetic energies to be where the work energy ends up. That's good. The solution included with the question deals with both.
 
Kindly see the attached pdf. My attempt to solve it, is in it. I'm wondering if my solution is right. My idea is this: At any point of time, the ball may be assumed to be at an incline which is at an angle of θ(kindly see both the pics in the pdf file). The value of θ will continuously change and so will the value of friction. I'm not able to figure out, why my solution is wrong, if it is wrong .
Thread 'Voltmeter readings for this circuit with switches'
TL;DR Summary: I would like to know the voltmeter readings on the two resistors separately in the picture in the following cases , When one of the keys is closed When both of them are opened (Knowing that the battery has negligible internal resistance) My thoughts for the first case , one of them must be 12 volt while the other is 0 The second case we'll I think both voltmeter readings should be 12 volt since they are both parallel to the battery and they involve the key within what the...
Thread 'Trying to understand the logic behind adding vectors with an angle between them'
My initial calculation was to subtract V1 from V2 to show that from the perspective of the second aircraft the first one is -300km/h. So i checked with ChatGPT and it said I cant just subtract them because I have an angle between them. So I dont understand the reasoning of it. Like why should a velocity be dependent on an angle? I was thinking about how it would look like if the planes where parallel to each other, and then how it look like if one is turning away and I dont see it. Since...
Back
Top