How to define kinetic energy of a compound system

AI Thread Summary
In a compound system like an Atwood machine, total kinetic energy can be defined by considering the motion of all connected masses as a single entity. When analyzing the kinetic energy of multiple moving parts, each object's energy should be calculated separately and then summed to find the total. For isolated systems, the relationship ΔK + ΔU = 0 applies, indicating that changes in kinetic energy are balanced by changes in potential energy. If the blocks are not connected, their kinetic energies are still added together to determine the system's total kinetic energy. Understanding these principles clarifies how to approach kinetic energy calculations in complex systems.
Davyd Sadovskyy
Messages
3
Reaction score
0
A system is defined as two connected masses in an atwood machine and the earth. How do I find total kinetic energy in a system where more than one object is moving (or is only one object actually moving since the two masses are connected with a string? idk)
upload_2017-11-3_21-30-10-png.png


This is an isolated system so... ΔK + ΔU = 0

How do I define energies of a system if there are multiple moving parts, each with its own energy? This is at the core of my confusion. I know that initially, there are no particles in this system with velocity, so Ki must be 0.
These are my questions

1.) How would you define the final kinetic energy? Do you treat the two moving blocks as a singly block instead of 2 separate blocks?

2.) What if a system consisted of 2 non connected blocks. How would you define final kinetic energy then?
 

Attachments

  • upload_2017-11-3_21-30-10-png.png
    upload_2017-11-3_21-30-10-png.png
    921 bytes · Views: 995
Physics news on Phys.org
Davyd Sadovskyy said:
How do I define energies of a system if there are multiple moving parts, each with its own energy?
Just add them together.

Davyd Sadovskyy said:
What if a system consisted of 2 non connected blocks. How would you define final kinetic energy then?
Just add them together.
 
The rope is tied into the person (the load of 200 pounds) and the rope goes up from the person to a fixed pulley and back down to his hands. He hauls the rope to suspend himself in the air. What is the mechanical advantage of the system? The person will indeed only have to lift half of his body weight (roughly 100 pounds) because he now lessened the load by that same amount. This APPEARS to be a 2:1 because he can hold himself with half the force, but my question is: is that mechanical...
Some physics textbook writer told me that Newton's first law applies only on bodies that feel no interactions at all. He said that if a body is on rest or moves in constant velocity, there is no external force acting on it. But I have heard another form of the law that says the net force acting on a body must be zero. This means there is interactions involved after all. So which one is correct?
Thread 'Beam on an inclined plane'
Hello! I have a question regarding a beam on an inclined plane. I was considering a beam resting on two supports attached to an inclined plane. I was almost sure that the lower support must be more loaded. My imagination about this problem is shown in the picture below. Here is how I wrote the condition of equilibrium forces: $$ \begin{cases} F_{g\parallel}=F_{t1}+F_{t2}, \\ F_{g\perp}=F_{r1}+F_{r2} \end{cases}. $$ On the other hand...
Back
Top