Finding the torque needed to accelerate a wheel

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Homework Help Overview

The problem involves calculating the torque required to accelerate a wheel with a specified mass and radius over a given time period. The subject area includes concepts of rotational dynamics, specifically torque, moment of inertia, and angular acceleration.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the calculation of angular acceleration and its units, questioning the original poster's approach to converting linear acceleration to angular acceleration. There is also a focus on the importance of including units in calculations to identify potential errors.

Discussion Status

The discussion is ongoing, with participants providing guidance on unit conversions and the necessity of including units in calculations. There is an acknowledgment of a potential error in the original poster's calculations, leading to a revised torque value from another participant.

Contextual Notes

There is a noted discrepancy in the radius value used by the original poster, which could affect the calculations. The discussion also highlights the importance of understanding the relationship between linear and angular measurements in the context of rotational motion.

Pablo
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Homework Statement



Object of fifty kg and a r= 0.025m. What's the torque to accelerate from 0 to 0.4 in 20s.

Homework Equations



Torque = Moment of inertia * angular acceleration
T = I * α

The Attempt at a Solution


[/B]
m = 50kg
r = 0.25m
α = (0.4) / 20 = 0.02

I = mr^2 = 50 * 0.25^2 = 3.125
T = I * α = 3.125 * 0.02 = 0.0625 Nm

I got 0.0625 Nm for my torque, but this does not match any of the choices. Am I doing something wrong?
 
Last edited:
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Welcome to the PF.
Pablo said:
α = (0.4) / 20 = 0.02
The units for angular acceleration should be in radians/s^2. How many radians are there in one revolution? :smile:
 
BTW, it's a good idea to carry units along in your calculations. That helps you to see errors like that early and correct them along the way. :smile:
 
berkeman said:
Welcome to the PF.

The units for angular acceleration should be in radians/s^2. How many radians are there in one revolution? :smile:

Wow, I can't forgot to multiply by 2 pi, thanks! I got 0.39Nm :)
 
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