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## Homework Statement

A computer disk drive is turned on starting from rest and has constant angular acceleration.

If it took 0.690s for the drive to make its second complete revolution, how long did it take to make the first complete revolution?

What is the angular acceleration?

## Homework Equations

w

^{2}= w

_{0}

^{2}+2[itex]\alpha[/itex]∅

∅=w

_{0}t+(0.5)[itex]\alpha[/itex]t

^{2}

## The Attempt at a Solution

I'm trying to first find the angular acceleration, and from there I can find out how long it took to make the first complete revolution.

First revolution:

w

_{0}=0 t=? [itex]\alpha[/itex]=[itex]\alpha[/itex] w=w ∅=2∏

Second revolution:

w

_{0}=w t=0.690s [itex]\alpha[/itex]=[itex]\alpha[/itex] ∅=2∏

Second revolution:

∅=w

_{0}t+(0.5)[itex]\alpha[/itex]t

^{2}

2∏ = w

_{0}(0.690)+(0.5)[itex]\alpha[/itex](0.690)

^{2}

[itex]\alpha[/itex]=[itex]\frac{2∏-w0(0.69)}{(0.5)(0.69)^2}[/itex]

First equation:

w

^{2}=w

_{0}

^{2}+2[itex]\alpha[/itex](2∏)

([itex]\frac{2∏-w0(0.69)}{(0.5)(0.69)^2}[/itex])([itex]\frac{2∏-w0(0.69)}{(0.5)(0.69)^2}[/itex])=2[itex]\alpha[/itex](2∏)

I rearranged to get:

4∏

^{2}=[itex]\alpha[/itex]((4∏(0.69)

^{2})+(π(0.69)

^{2})-((0.5)(0.69)

^{2}))

[itex]\alpha[/itex]=5.45