# Moment of Inertia Problem

• Digdug12

## Homework Statement

A wheel, with circumference 0.6 m and moment of inertial 43 kg m2 about its center, rotates about a frictionless axle with angular velocity 13 radians per second. A brake is applied which supplies a constant force to a point on the perimeter of the wheel of 9 N, tangent to the wheel and opposing the motion. How many revolutions will the wheel make before coming to rest?

## Homework Equations

KErotational=I*Omega2
Torque=I*alpha
I=M*R2

## The Attempt at a Solution

I'm lost at how to start this problem, I tried to get the deceleration caused by the 9N force applied on the wheel by Newton's Second Law but I couldn't get the mass, so i used the I=M*R2 equation to get the mass and then used F=M*a to find the deceleration, took that answer and divided by 2pi to find the revolutions, but the answer was off. What am I missing?

The angular deceleration is given by $a= \alpha r$. Find $\alpha$. Then use the equations of rotational motion to find the total angular displacement from the initial angular velocity to rest.

I used a=alpha*r and i got the alpha to be .003, using Omegaf2=Omegai2+2*alpha*Theta i get 28166, but the answer should be 672.9

EDIT: nevermind, i got it, thanks!

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