Flywheel of a steam engine problem

[Paged]

Homework Statement

The flywheel of a steam engine runs with a constant angular speed of 156rev/min. When the steam is shut off, the friction of the bearings and of the air brings the wheel to rest in 2.20h. What is the tangential linear acceleration of a particle 52.4cm from the axis of rotation when the flywheel is turning at 72.5rev/min.

Homework Equations

At= r(alpha)

I know what the radius is, so I must find angular acceleration.

alpha = (Wf-Wi)/t
_____=(0-156)/(2.2*60)
_____=-1.18rev/min^2

Therefore

At= (52.4cm)(-1.18rev/min^2)


3. The attempt at confusion

So now that I am done, I am left wondering why someone would put 72.5 rev/min in the equation. I was tempted to put that into my equation to find alpha, but then I am lacking time. I then turned towards my linear equivalent equations, but I am lacking time it takes to decelerate to 72.5 or the amount of rotations it takes to get that far. What am i meant to do?

 

[Dick]

Its not unheard for a problem to contain extraneous information. You've correctly figured that the tangential acceleration is constant and you don't need the speed. If there is a followup question asking you to compute the radial acceleration? Then you will need the speed.

 

[Paged]

Yeah the next one was calculate the total force, so I realized that the speed was simply used in omega^2(r), so that cleared it up. Thanks though, it had me for a bit