Maximizing Projectile Motion: Finding the Optimal String Cut Location

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Homework Help Overview

The discussion revolves around a problem in projectile motion involving a mass attached to a massless string, which swings in a vertical circle. The objective is to determine the optimal location to cut the string so that the mass's projectile motion reaches its maximum height directly above the center of the circle.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the conditions for the mass to maintain minimum speed at the top of the circle and explore the relationship between tension, gravitational force, and velocity. There are attempts to derive equations related to energy conservation and projectile motion, with questions about differentiating the height with respect to the angle.

Discussion Status

Some participants have provided equations and attempted to clarify their reasoning, while others express confusion and seek further explanation. There is an ongoing exploration of the necessary conditions for the mass's motion and the implications of cutting the string at different points.

Contextual Notes

Participants are working under the assumption that the mass must have sufficient speed at the top of the circle to prevent the string from going slack. There is a focus on the energy considerations at the moment of escape and the maximum height of the projectile.

oscar_lai_hk
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A mass is attached to one end of the massless string, the other and of which is attached to a foxed support. The mass swings around in a vertical circle as shown in Fig 5.36. Assuming that the mass has the minimum speed necessary at the top of the circle to keep the string from going slack, at what location should you cut the string so that the resulting projectile motion of the mass has its maximum height located directly above the center of the circle.
 
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oscar_lai_hk said:
A mass is attached to one end of the massless string, the other and of which is attached to a foxed support. The mass swings around in a vertical circle as shown in Fig 5.36. Assuming that the mass has the minimum speed necessary at the top of the circle to keep the string from going slack, at what location should you cut the string so that the resulting projectile motion of the mass has its maximum height located directly above the center of the circle.

Hi oscar_lai_hk! :smile:

Show us what you've tried, and where you're stuck, and then we'll know how to help. :smile:
 
tiny-tim said:
Hi oscar_lai_hk! :smile:

Show us what you've tried, and where you're stuck, and then we'll know how to help. :smile:

I can write the equation towards the center : T + mg cos0 = mv^2/R
and I consider the energy at the moment of escape and the highest position
I get the equation (0.5)mv^2 = (0.5)m(vcos0)^2 + mgy
then I try to diff. the above equation of y respect to the angle 0
it is right?
 
oscar_lai_hk said:
I can write the equation towards the center : T + mg cos0 = mv^2/R
and I consider the energy at the moment of escape and the highest position
I get the equation (0.5)mv^2 = (0.5)m(vcos0)^2 + mgy
then I try to diff. the above equation of y respect to the angle 0
it is right?

Hi oscar_lai_hk! :smile:

I'm really not following that. :confused:

Start by putting T = 0 at the top of the loop to find out what vtop is.

Then find out what vθ is, at any angle θ.

The split vθ into horizontal and vertical components … :smile:
 

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