# Something weird about Rotational Kinematic Equations

## Homework Statement

I need to find the average acceleration of a gramophone record.

Initial angular velocity, W = 0
Final angular velocity, w = 3.50rad s^-1

## Homework Equations

The equation given by the answer is

t= 8/w
a = ( w - W ) / t

## The Attempt at a Solution

This is the equation I use

w2 = W2 + 2a8

But if I multiply it with 2, the angular acceleration will become 49rad s-2

That mean my equation will become
w2 = W2 + a8

Can anyone explain this to me?
Or I use a wrong equation?

## Homework Equations

The equation given by the answer is

t= 8/w
a = ( w - W ) / t

## The Attempt at a Solution

This is the equation I use

w2 = W2 + 2a8

You are right:

t= 8/w is wrong because the angular velocity is not constant

It should be t= 28/w

ok...thx... ^^

tiny-tim
Homework Helper

## Homework Equations

The equation given by the answer is

t= 8/w
a = ( w - W ) / t