Calculating Torque for LP Turntable with Given Angular Speed and Mass

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Homework Help Overview

The problem involves calculating the torque required for an LP turntable to reach a specified angular speed of 3.53 rad/s over a distance of 1.9 revolutions, starting from rest. The turntable is described as a uniform disk with a diameter of 30.7 cm and a mass of 0.24 kg.

Discussion Character

  • Exploratory, Conceptual clarification, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the need to find angular acceleration to calculate torque and question how to derive time from the given parameters. There is a focus on understanding the definitions of acceleration and average speed in the context of angular motion.

Discussion Status

Participants are actively engaging with the problem, exploring definitions and relationships between angular speed, acceleration, and time. Some guidance has been provided regarding the calculation of average speed, but the discussion remains open with no consensus on the approach to finding time.

Contextual Notes

There is a noted lack of information regarding the time taken to reach the final angular speed, which is critical for solving the problem. Participants are working within the constraints of the given data and attempting to derive necessary values from it.

cstout
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Homework Statement



An LP turntable must spin at 3.53 rad/s to play a record. How much torque must the motor deliver if the turntable is to reach its final angular speed in 1.9 revolutions, starting from rest? The turntable is a uniform disk of diameter 30.7 cm and mass 0.24 kg.

Homework Equations



T=rF
F=ma
Theda = (Angular Acceleration (t^2)) / 2

The Attempt at a Solution



I tried using the above equations but I'm not sure about finding the angular acceleration to find the the final Torque.
 
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What's the most basic definition of acceleration? That's what you need here.
 
change in distance / change in time
 
cstout said:
change in distance / change in time
That's the definition of velocity. What's the similar definition of acceleration?
 
oh yea, sorry, change in velocity / change in time
 
cstout said:
oh yea, sorry, change in velocity / change in time
Good. So the angular acceleration is the change in angular velocity over time.

But I just realized that they didn't give you the time--I misread the problem. (D'oh!) So you'll need to use another approach to find the time.

Try this: What's the average speed of the turntable while it's accelerating? Use that--and the distance--to calculate the time. (Change revolutions to radians.)
 
Ok, so the Time = Distance / Average Speed, the distance is 11.932 radians, but what is the average speed, is it simply the given speed of 3.53 or something else?
 
cstout said:
but what is the average speed, is it simply the given speed of 3.53 or something else?
No. 3.53 rad/s is the final speed and 0 is the initial speed. So what's the average speed?
 

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