# Angular motion homework problem

## Homework Statement

An electric motor rotating a workshop grinding wheel at a rate of 90 rev/min is switched off. Assume constant negative angular acceleration of magnitude 2.50 rad/s2.
(a) How long does it take for the grinding wheel to stop?

(b) Through how many radians has the wheel turned during the interval found in (a)?

## Homework Equations

wf=wi+at^s
theta= 1/2 (wi+wf)t

## The Attempt at a Solution

I got the right answer for (a) which was 3.77 sec so for (b) I thought that all you needed to do was plug in the values into the second equation to get theta but the answer I got was wrong. I got -17.766.....I don't know what I'm doing wrong...any help would be appreciated.

## Answers and Replies

uuh lol never mind i just had an extra negative sign