This is Giancoli Answers with Mr. Dychko. The angular displacement of this centrifuge is the average angular velocity multiplied by time. So we have final angular velocity plus initial angular velocity over 2 multiplied by time and it starts from rest so ω i is 0. Well, we have to do some work with units here because we are given revolutions per minute for the final angular velocity of 15000 revolutions per minute. So we are taking 15000, dividing it by 2— since ω i is 0, it's just 15000 for ω f— divide by 2 and then multiply that by 4 minutes and I converted this 240 seconds into minutes by multiplying by 1 minute for every 60 seconds so that the revolutions per minute multiplied by minutes leaves us with revolutions and so we have 3.0 times 10 to the 4 revolutions.

COMMENTS

By carolsilber on Thu, 5/5/2016 - 12:55 AM

wouldnt it be 3.0x10^5 because the answer is 30,000

By Mr. Dychko on Tue, 5/10/2016 - 5:25 AM

Hi carolsilber, thanks for asking. $30,000$ is written as $3.0 \times 10^4$ , so it doesn't look like there's any problem here. Let me know if you suspect any other errors though.

All the best,
Mr. Dychko

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