- #31
Shahid0072
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Tiny tim...Which equations?
Calculating Angular Velocity and Time for Insect on Rotating Rod
- Thread starter Shahid0072
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Homework Help Overview
The discussion revolves around a physics problem involving a rotating rod and an insect that lands on it. The rod is pivoted at its midpoint, and the insect falls vertically onto the rod while moving towards one end. The problem requires calculating the speed of the insect and the time it takes to reach the end of the rod while maintaining a constant angular velocity of the rod.
Discussion Character
- Mixed
Approaches and Questions Raised
- Participants explore the conservation of angular momentum and its implications for the system's angular velocity and moment of inertia as the insect moves. Questions arise regarding the effects of torque due to the insect's weight and how these factors interact to maintain constant angular velocity.
Discussion Status
Participants are actively engaging with the problem, discussing various aspects of angular momentum and torque. Some have offered insights into the relationships between the insect's movement, the rod's rotation, and the conservation laws, while others express uncertainty about the presence of external torque and its effects. There is no explicit consensus yet, but the discussion is progressing with multiple interpretations being explored.
Contextual Notes
The problem involves specific parameters such as the mass of the insect and rod being equal, and the length of the rod is given as 1.8 meters. Participants note the complexity of the problem and the need for careful consideration of the forces and torques involved.
- #32
tiny-tim
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Do you mean you can't read the symbols below?
(if you can, just copy one and paste it
)
(if you can, just copy one and paste it
)- #33
Doc Al
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Moderator's note: Moving to Intro Physics, since this is more about solving a particular problem than about broader conceptual issues.
- #34
Shahid0072
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M writing thru my cell..Its not allowing me to click on those letters..I can just c them
- #35
tiny-tim
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Shahid0072 said:
The equation which relates the speed V to the angular velocity ω,
and the τ = ωdI/dt equation
(with all the numbers, please
).- #36
Shahid0072
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I wrote it..We are just given Length of rod (L)in numbers which is 1.8 m..And i wrote already that ¥(angular velocity)=12V/7L..We have to calculate V in nos..
- #37
Shahid0072
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Tim..Torque is variable..We know change in angular momentum ..What can we do?
- #38
tiny-tim
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Shahid0072 said:
Call the position of the insect x, and the angle θ, and find the moment of inertia as a function of x, and the torque as a function of x and θ.
- #39
Shahid0072
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I guess u haven't read my earliear post..Torque varies as Mgx cos§ where x is insect's distance from centre and § is angle rotated by rod..Initial moment of inertia of rod +insect is 7MLL/12 AND when rod is vertical is MLL/3..How to calculate V in numbers?
- #40
tiny-tim
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Shahid0072 said:
hmm … that can't be right … 1/3 < 7/12, but the moment of inertia should be increasing.
If L is the length AB of the whole rod, then I for the rod is 1/12 ML2, to which you have to add I for the insect for L/4 ≤ x ≤ L/2.
- #41
Shahid0072
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Oh..Pardon..Its 7MLL/48 Instead of 7MLL/12..Sorry..But what can we do to calculate V?
- #42
tiny-tim
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Shahid0072 said:
That's better!
ok, then, as you said …
Now use τ = 12V/7L dI/dt.
- #43
Shahid0072
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But torque is variable??
- #44
Shahid0072
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Its a function of both x and § as stated earlier..How can we find V in numerals by using that!