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I was able to solve this problem fine, but I had a question about it:

"A disk 8.00 cm in radius rotates at a constant rate of 1200 rev/min about its central axis. Determine (a) its angular speed, (b) the tangential speed at a point 3.00 cm from its center, (c) the radial acceleration of a point on a rim, and (d) the total distance a point on the rim moves in 2.00 s."

In solving the problem, I first converted the given information to SI units.

In solving for (a), the angular speed is given. It's only the conversion that was necessary, so a = 125.6 rad/s. In solving for b, I realized that tangential speed (v) = rw (where w is the greek letter omega, representing angular velocity). Multiplying the r and w gives you 3.79 m/s. Part C is where my question lies: I understand that radial/centripetal acceleration = v^2/r which = rw^2. If I plug in the given values for v^2/r (3.79^2/0.08), I don't get the right answer. If I plug in the values for rw^2, I do. If they're equivalent to each other, how come the answers aren't matching up?

Thank you.

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# Homework Help: Rotational Dynamics of a disk

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