# Rotational Motion

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

a=w/t

## 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?

## Answers and Replies

Homework Helper
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.