Calculate Angular Acceleration of Rotational Motion: 4.9rev in 1s

[islanderman7]

Homework Statement

A tire placed on a balancing machine in a service station starts from rest and turns through 4.9 revolutions in 1.0 s before reaching its final angular speed. Calculate its angular acceleration.

I need my answer in
rad/s^2

Homework Equations

a=w/t
1rev= 2n rad

The Attempt at a Solution

Converted rev/s to rad/s
4.9rev/s * (2n rad/s)/ 1 rev= 30.7876 rad/s

a=w/t
a= (30.7876 rad/s)/ 1sec => 30.7876 rad/s^2

This answer comes out wrong.

What am I doing wrong?

 

[Dick]

It's not a constant angular velocity question. Angular velocity changes with time, so you can't just use a=w/t. You need a formula analogous to s=(1/2)*a*t^2 for linear motion. It looks very similar, just the meaning of the letters changes.

 

[islanderman7]

Okay thanks. I get it now.