Unsure about formula for kinetic energy

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Homework Help Overview

The discussion revolves around the application of the kinetic energy formula in a scenario involving a flagpole and a falling ball. Participants explore the conditions under which the formula can be applied and the implications of the setup on the velocity vector of the falling object.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the validity of using the kinetic energy formula under specific conditions, such as neglecting the mass of the pole and the relative sizes of the ball and pole. Questions arise regarding the direction of the velocity vector and the implications of the angle theta in the context of potential and kinetic energy.

Discussion Status

There is an ongoing exploration of the assumptions related to the problem setup, with some participants providing guidance on the conditions for applying the formula. Multiple interpretations of the velocity vector's direction and the implications of the angle theta are being examined, indicating a productive dialogue without explicit consensus.

Contextual Notes

Participants note the importance of the mass and dimensions of the objects involved, questioning the appropriateness of the formula based on these factors. There are also references to previous discussions that inform the current understanding of the problem.

Warlic
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Imagine the flagpole and ball with mass m fall together. Can I here use the formula mg*l*sin(theta)=(1/2)*mv^2
If I can, in what direction will the velocity vector be - is it going to be tangential to the flagpole?
 
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You can use the formula, if

1) the mass of the pole can be neglected and
2) the diameter of the ball is much smaller than the length of the pole.

The velocity vector would be perpendicular to the pole (but I think that's what you ment).
 
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stockzahn said:
You can use the formula, if

1) the mass of the pole can be neglected and
2) the diameter of the ball is much smaller than the length of the pole.

The velocity vector would be perpendicular to the pole (but I think that's what you ment).
"the diameter of the ball is much smaller than the length of the pole."
Why is this?
 
Your equation is incorrect. What does it tell you when theta is zero? Try again.

Also, what idiot made up this problem. The US flag should never be shown disrespectfully falling down!

Chet
 
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For the same reason as discussed yesterday. This formula couldn't be applied for the pole because each slice dm moves with a different velocity depending on the position. If the diameter of the ball would have a similar value as the length of the stick, then you would have to take the different slices of the ball into account. If the stick is much longr, than you can consider all slices of the ball moving with the same velocity.
 
stockzahn said:
For the same reason as discussed yesterday. This formula couldn't be applied for the pole because each slice dm moves with a different velocity depending on the position. If the diameter of the ball would have a similar value as the length of the stick, then you would have to take the different slices of the ball into account. If the stick is much longr, than you can consider all slices of the ball moving with the same velocity.
Alright, thank you, I think I get the idea now
 
Chestermiller said:
Your equation is incorrect. What does it tell you when theta is zero? Try again.

Also, what idiot made up this problem. The US flag should never be shown disrespectfully falling down!

Chet
It tells me there is zero potential energy at that point, everything is turned into kinetic energy?
 
Warlic said:
It tells me there is zero potential energy at that point, everything is turned into kinetic energy?
According to your equation, the velocity is zero when theta is equal to zero.
 
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