A wheel free to rotate about its axis that is not frictionless is initially at rest. A constant external torque of +40 N·m is applied to the wheel for 24 s, giving the wheel an angular velocity of +610 rev/min. The external torque is then removed, and the wheel comes to rest 120 s later. (Include the sign in your answers.)(adsbygoogle = window.adsbygoogle || []).push({});

(a) Find the moment of inertia of the wheel.

kg·m2

(b) Find the frictional torque, which is assumed to be constant.

N·m

This whole topic of angular/moment of inertia and torque taking its toll on me. Please bear with me, the more I read in textbook the more confused I get.

Relevant Equations:

Inertia = sum of mi * ri^2

Inertia for continuous objects = integral of r^2 dm

I would use the equation for inertia for continuous objects correct? since the textbook used the other one when given points.

The problem doesn't give us any masses/radius -- How would I start this?

For part B:

relevant equations:

Torque = r x F

Tnet = I alpha

What should I use for the Moment of Inertia for the wheel? It doesn't state it,

some exercise from the book says consider a wheel of a bicycle to be a hoop I = MR^2

Im not sure if this is correct,

I did for translation equation

Fnet = Ma

Ext F + friction = Ma

For rotation

Tnet = I alpha

RF - Rf = 1/2 M R^2 (a/R)

= F-f = 1/2 Ma

I added the two equations

2F = 3/2 Ma

a = 4F/3M

From equation 1

F+f = Ma

f = F/3

Is this even remotely correct?

Please help, thanks so much.

1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

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# Homework Help: Moment of Inertia and Torque

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