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1. The problem statement, all variables and given/known data

The flywheel of a steam engine runs with a constant angular speed of 146 rev/min. When steam is shut off, the friction of the bearings and the air brings the wheel to rest in 1.2 h.

A.) What is the magnitude of the constant angular acceleration of the wheel in rev/min2?

B.) How many rotations does the wheel make before coming to rest?

C.) What is the magnitude of the tangential component of the linear acceleration of a particle that is located at a distance of 60 cm from the axis of rotation when the flywheel is turning at 73.0 rev/min?

D.) What is the magnitude of the net linear acceleration of the particle in the above question?

2. Relevant equations

Alpha = Change in W/Change in T

At = alpha * r

Theta = Theta initial + W initial + (alpha * T)/2

V = WR

A = (Vf - Vo)/T

3. The attempt at a solution

This is a problem we did on a previous homework but I am trying to do it again to study for my test tomorrow but I am not understanding why I am doing what.

A.) Alpha = Change in W/Change in T

(146rev/min)/72 min = 2.03 rev/min^2

I though that W had to be in rad not rev for the equation to work. I know it asks for it in rev/min^2 so W can be in rad/min and rev/min???

B.) Theta = Theta initial + W initial - (alpha * T)/2

Why do I change it to - alpha? Is it because it is slowing down?

146 rev/min * 72 min - (2.03 rev/min^2 * 72^2)/2 = Theta

So we use W as rev/min not radians because thats what we used previously?

C.) At = Alpha * r

(2.03 * 2pi/3600) * .60 = .21 cm/s^2

Now why are we dividing by 3600 and not just 60? I thought we were trying to get it to seconds so why is not just 60? Why are we NOW changing alpha to rad??? Why can't we use rev like we have been? I am getting myself so confused now!

D.) I haven't started to look over this one yet I just really need help with A-C

Thanks so much!!!

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# Homework Help: OMG Test Tomorrow Please help!

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