Find RPM at which Lower Cord Goes Slack in Figure 5.72

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Homework Help Overview

The problem involves determining the revolutions per minute at which a lower cord goes slack in a given physical setup. The context relates to dynamics and tension in cords during rotational motion.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to clarify the conditions under which the lower cord remains tight and questions whether the critical point is when the tension becomes zero. Other participants engage by confirming this understanding and discussing the implications of tension being zero.

Discussion Status

The discussion is active, with participants validating the original poster's interpretation of the problem. There is a focus on the relationship between tension and the number of revolutions, with some guidance offered regarding setting up equations based on the tension condition.

Contextual Notes

Participants are navigating the assumptions related to the tension in the cords and the specific conditions under which the lower cord transitions to slack. There is an emphasis on understanding the limit of revolutions before slack occurs.

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Homework Statement



In http://session.masteringphysics.com/problemAsset/1007030/9/yf_Figure_5_72.jpg I have to find the number of revolutions per minute at which the lower cord goes slack.

The Attempt at a Solution



I just need to be sure: What they are asking me to find is the number of revolutions, so the lower cord is still tight, but it's the limit - so if the revolutions is a teeny weeny bit smaller, it goes slack?

If I have understood it correctly, is this the number of revolutions at which the block is only affected by the upper cord, and then the number of revolutions has be to bigger than that number? I hope you get me.

Thanks in advance.
 
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Sounds to me like you understand what's being asked. At the point where the lower cord just barely goes slack, what is its tension?
 
it is zero? :-)
 
- I mean, the text says "... just goes slack", so it is slack and thereby zero?
 
Niles said:
it is zero? :-)
Exactly. So set up your equations, set that tension equal to zero, and turn the crank.:smile:
 

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