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Physics/To shift a weight


I'm not a student, but a young man of nearly 75 years as a hobby he enjoys studying a bit 'of physics and mathematics.
I wonder if you would help me with a problem I asked myself.
So I have a weight (ideally point) resting on the floor (say a weight of 80kg), I want to shift this burden to 5 meters
pulling it with a rope (it is not appropriate to say that the rope is attached to its center of gravity because I assumed a point weight).
I do not know the coefficient of friction between the weight and the floor.
Of course I will to move this weight pulling the rope, I would minimize my physical effort (but it would be the same if I might be an electric motor,
I would like to minimize the motor consumption ...).
Now I can place in such a way that the rope forms an angle of 0 with the floor (virtually parallel to the floor),
or I can position so that the angle between the rope and the floor is of 10 , 20 , 30 etc. in short, to my liking.
What will be the angle between the rope and the floor that minimizes the effort?
I understand that the effort (work) is also a function of time ...,
How long do you want to shift this burden to 5 meters?
Then you will also get the time: I want to move a weight of 80 kg to 5 meters in 15 seconds, what will be the ideal angle that minimizes my job
(75 years old)?

The problem is more complex than you might think.  If you're trying to minimize the work done, then the way to do it is to pull up on the weight at just under 90 degrees and let it swing.  Barring the ability to get high above it, you would want to repeatedly swing it from heights you can get to.  You would do minimal work, because you would eliminate friction entirely.  That's the ideal way.  

If you can't lift it, then you run into a constrained situation where your maximum force that you can pull with comes into play.  At that point, you have to figure out how much force you can apply to it, you might not be able to drag it at all!

The actual formula for the answer is a pretty standard one for students to work out, I've used that problem in class for years.  However, it depends on the coefficient of friction, so there's no way to use it.


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Dr. Stephen O. Nelson


I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.


I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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