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Unformatted text preview: Chapter 10 solved problems NOTE: A few of the problems here have slightly different numerical values than in the book but the solution is the correct one with the values given here. 8. Picture the Problem : The Earth rotates once on its axis every 24 hours. Strategy: Convert the known angular speed of 1 rev/day into units of radians per second. Solution: Convert the units: Insight: This angular speed corresponds to about 15° / hour. A “rule of thumb” in astronomy is that the “fixed” stars will move across the sky at this rate (1° every 4 minutes, or 15 arcsec/s) due to Earth’s rotation. 19 . Picture the Problem : The ceiling fan rotates about its axis, slowing down with constant angular acceleration before coming to rest. Strategy: Use the kinematic equations for rotation (equations 108 through 1011) to find the number of revolutions through which the fan rotates during the specified intervals. Because the fan slows down at a constant rate of acceleration, it takes exactly half the time for it to slow from 0.90 rev/s to 0.45 rev/s as it does to come to a complete stop. Solution: 1. (a) Apply equation 109 directly: ( 29 ( 29 ( 29 1 1 2 2 0.90 rev/s 2.2 min 60 s min 59 rev t θ ϖ ϖ ∆ = + = + × = 2. (b) Apply equation 109 directly: ( 29 ( 29 ( 29 1 1 2 2 0.45 0.90 rev/s 1.1 min 60 s min 45 rev t θ ϖ ϖ ∆ = + = + × = Insight: An alternative way to solve the problem is to use equation 108 to find 2 0.0068 rev/s α =  and use α in equation 1011 to find θ ∆ for each of the specified intervals. Note that you can stick with units of rev/s 2 to find θ ∆ in units of revolutions instead of converting to radians and back again....
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This note was uploaded on 01/05/2012 for the course CHEM 3321 taught by Professor Bean during the Spring '11 term at American Jewish University.
 Spring '11
 BEAN

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