Find RPM at which Lower Cord Goes Slack in Figure 5.72

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In summary, the conversation is about finding the number of revolutions per minute at which the lower cord goes slack. The person asking the question is confirming if they understand the problem correctly and clarifying the tension of the lower cord when it goes slack. The expert confirms that the tension is indeed zero and advises to set up equations and solve for the number of revolutions.
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Niles
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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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  • #2
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?
 
  • #3
it is zero? :-)
 
  • #4
- I mean, the text says "... just goes slack", so it is slack and thereby zero?
 
  • #5
Niles said:
it is zero? :-)
Exactly. So set up your equations, set that tension equal to zero, and turn the crank.:smile:
 

1. What is the purpose of finding the RPM at which the lower cord goes slack in Figure 5.72?

The purpose of finding the RPM at which the lower cord goes slack in Figure 5.72 is to determine the maximum rotational speed that can be applied to the object without causing tension in the lower cord. This information is important in designing and operating machines or equipment that involve rotational motion.

2. How is the RPM at which the lower cord goes slack calculated?

The RPM at which the lower cord goes slack can be calculated by dividing the length of the lower cord by the circumference of the rotating object and then multiplying by 60 to convert the result to revolutions per minute (RPM).

3. What factors can affect the RPM at which the lower cord goes slack?

The RPM at which the lower cord goes slack can be affected by the length of the lower cord, the weight of the rotating object, and the tension or stiffness of the cord. Other factors such as friction, air resistance, and the shape of the rotating object can also play a role.

4. How can the RPM at which the lower cord goes slack be used in real-world applications?

The RPM at which the lower cord goes slack is a crucial factor in designing and operating various machines and equipment, such as conveyor belts, pulley systems, and rotating machinery. It helps determine the maximum safe speed for the equipment, preventing potential accidents or damage.

5. What precautions should be taken when determining the RPM at which the lower cord goes slack?

When determining the RPM at which the lower cord goes slack, it is important to ensure that all measurements are accurate and precise. The equipment should be operated within the recommended safety limits, and caution should be taken to avoid any potential hazards. If necessary, a professional should be consulted for accurate calculations and safe operation of the equipment.

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