Finding Kinetic Energy and Velocity of a pulley / block system

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Homework Help Overview

The problem involves a pulley-block system where a hanging block is attached to a pulley. The pulley has a specified mass and radius, and the block is released from a certain height. The main focus is on finding the kinetic energy of the system and the speed of the block just before it hits the ground.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the relationship between potential energy and kinetic energy in the system, with one participant noting the equation setup. Questions arise regarding the moment of inertia of the pulley and its dependence on the hanging mass. There is also uncertainty about how to solve for the kinetic energy given the presence of multiple unknowns.

Discussion Status

The discussion is ongoing, with participants providing insights into the moment of inertia of the pulley. However, there remains a lack of consensus on how to proceed with solving for the kinetic energy and velocity, as multiple unknowns complicate the equation. Guidance has been offered regarding the moment of inertia, but further clarification is needed on how to integrate this into the kinetic energy calculations.

Contextual Notes

Participants are navigating the complexities of the problem, including the need to account for both the pulley and the hanging mass in their calculations. There is an emphasis on understanding the relationships between the variables involved without providing direct solutions.

pyranos
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Homework Statement


In the problem, a hanging block, m, is attached to a pulley that is mounted on a horizontal axle with negligible friction. The pulley has a mass of M=75kg and a radius of R=6.0cm. The mass of the hanging block is m=1kg. The block is released from rest at a height above the ground of 50cm without the cord slipping on the pulley. The pulley is a uniform disk.


Homework Equations


A) What is the Kinetic Energy of the system right before the block hits the ground?
B) What is the speed of the block right before it hits the ground?

The Attempt at a Solution


I understand that the potential energy of the system in the beginning will be equal to the kinetic energy of the system just before the block hits the ground, however, I do not know how to find the moment of inertia of the system or the velocity of the block.

I have this equation setup:
PE = KE
mgh = 1/2(m)(v^2) + 1/2(I)(ω^2)

I am not sure where to even start since I don't know how to find the moment of inertia, I, or omega. Anything would help out, even a little nudge in the right direction would be appreciated.
 
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Moment of inertia of pulley = moment of inertia of a uniform disc = \frac{1}{2}Mr^{2}.
 
grzz said:
Moment of inertia of pulley = moment of inertia of a uniform disc = \frac{1}{2}Mr^{2}.

Would the hanging mass affect the moment of inertia on the disc?
 
I understand that the moment of inertia for the disc is 1/2(M)(r)^2, but how do you solve the equation for KE? There are two unknown variables still in the equation, and I am not sure how to solve for velocity or omega.
 

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