What Angle Does a Bob in an Accelerating Train Make with the Vertical?

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Homework Help Overview

The problem involves a bob suspended in a train that is accelerating, specifically at an acceleration of g/√3. The discussion centers on determining the angle the bob makes with the vertical from the perspectives of two observers: one inside the train and one on the platform.

Discussion Character

  • Mixed

Approaches and Questions Raised

  • Participants explore the implications of acceleration on the observed angle of the bob, considering the effects of pseudo forces. Questions arise regarding the consistency of observations between the two observers and the mechanics of light and visibility in this context.

Discussion Status

The discussion is ongoing, with participants questioning the observations made by the two observers and whether they would agree on the angle of the bob. Some guidance has been offered regarding the interpretation of the angle, but no consensus has been reached.

Contextual Notes

There is uncertainty about the specific angles observed by each participant and how the setup of the problem influences their observations. The original poster expresses doubt about the applicability of their initial conclusion to both parts of the question.

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Homework Statement


A bob of mass m is suspended from the ceiling of a train moving with an acceleration g/√3
(a) If an observer is sitting inside the train, what angle with the vertical will he observe?
(b) If an observer is standing on the platform, what angle will he observe?

Homework Equations

The Attempt at a Solution


I know that the angle is 30 degrees (after taking the pseudo force into account), but I'm not sure if this is the answer for both parts or just (b)?
 
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If there is a protractor sticking down from the train's ceiling, will the 2 observers agree with the rope's alignment?
 
I don't know, that's the issue.
 
One guy sees the rope in front of (obscuring) the 30° mark ... how could the other guy see a different number being blocked?
The light either gets blocked, or it doesn't.
 
So they both see the same thing. Okay!
 

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