An object is spinning at 4 rev/s and starts deccelarting at .9 rev/s^2. How long will it take the object to stop?

Answer 1

a = -.9(2pi) rad/s^2
then
v = -.9(2pi)t + c
when t=0, v=4(2pi)
so c= 8pi
then v = (-1.8pi)t + 8pi
we want v = 0
0 = (-1.8pi)t + 8pi
t = 40/9 seconds

or

just thinking about it, it loses .9revs per second, so 4/.9 = 40/9

(sometimes thinking within the box gets you trapped in the box)