Posted by **need help as soon as possible** on Wednesday, March 23, 2011 at 2:35pm.

A clothes dryer is spinning at 75 rpm. A student opens its door and it comes to rest after rotating through four revolutions. Assume constant deceleration. What was the magnitude of the dryer's angular deceleration?

- physics -
**Damon**, Wednesday, March 23, 2011 at 3:22pm
Vi = 75 * 2 pi radians/min *1 min/60 sec

= 5 pi/2 radians/second

v = Vi - a t

0 = 5 pi/2 - a t

so t = 5 pi/2a

4*2pi = Vi t + (1/2) a t^2

8 pi = ( 5 pi/2)(5 pi/2a) + (1/2)a (5 pi/2a)^2

etc

- sign repair -
**Damon**, Wednesday, March 23, 2011 at 3:28pm
Vi = 75 * 2 pi radians/min *1 min/60 sec

= 5 pi/2 radians/second

v = Vi - a t

0 = 5 pi/2 - a t

so t = 5 pi/2a

+++++++++ a is assumed negative +++

4*2pi = Vi t - (1/2) a t^2

8 pi = ( 5 pi/2)(5 pi/2a) - (1/2)a (5 pi/2a)^2

8 pi a = (5 pi/2)^2 = (1/2)(5 pi/2)^2

8 pi a = (1/2)(5 pi/2)^2

16 pi a = 25 pi^2/4

a = (25/64) pi

remember it is negative (deacceleration)

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