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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