# Rotational Kinematics

#### nautica

A phonograph record slows from an initial 45 rpm at a rate of .05 rad/s^2.

a) how long does it take to come to rest???

orig rotational velocity = 45 rpm = 4.71 rad/sec

t = 94.2 s

b) How many revolutions does it make before stopping???

35.31 rev

Last one for the week. How does this look???

Thanks agaiin
Nautica

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#### arcnets

I think it's correct.

Here's a shorter and more precise way to do (b):

Without slowing down, you get
45*94.2/60 = 70.65 revolutions.
When slowing down, you know the answer is half of that:
35.325 revolutions.

#### nautica

Thanks, but for some reason the longer version makes more sense to me.

Nautica

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