Acceleration on inclined plane

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Discussion Overview

The discussion revolves around determining the acceleration of a block on an inclined plane that is itself accelerating in the +Y direction. Participants explore different approaches to analyze the problem, considering various frames of reference and methods from classical mechanics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant, Alex, seeks a formula for the acceleration of a block on an inclined plane that is accelerating, expressing uncertainty about the appropriate frame of reference and free body diagram.
  • Another participant questions whether the acceleration of the plane is given or needs to be determined by the block's forces, suggesting that if it is given, the total acceleration can be found by vector addition.
  • A different participant believes that Newtonian mechanics can be applied, assuming the plane's acceleration refers to its entire motion rather than just the center of mass, and mentions constraints that might prevent rotation.
  • One participant proposes using the accelerating frame of the incline and incorporating an inertial pseudo force due to the plane's acceleration.
  • Another participant suggests redefining gravitational acceleration to account for the plane's upward acceleration, indicating that the problem can be solved as if the plane were stationary, followed by vector addition to find the total acceleration.

Areas of Agreement / Disagreement

Participants express various methods and considerations for solving the problem, but there is no consensus on a single approach or resolution of the uncertainties involved.

Contextual Notes

Participants mention different assumptions regarding the nature of the inclined plane's acceleration and its implications for the analysis, as well as the potential need for constraints to be defined.

bongobl
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Hi guys I am trying too find a formula to figure out how I would find the acceleration of a block on an incline plane IF that plane itself were accelerating in the +Y direction.
I am not even sure which frame of reference to use since the acceleration is in 2 dimensions. This hinders me from being able to draw a free body diagram

Does anybody know how to go about finding the acceleration of the block (in cartesian vector form)?
Thanks
-Alex
 

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Is the acceleration of the plane given, or is it to be determined by the force from the block?

If it is given then just remember that acceleration is a vector. So you can just add the known acceleration of the plane to the unknown acceleration of the block relative to the plane to get the total acceleration and you can still write Newton's 2nd law. The movement of the plane shouldn't change the free body diagram at all.

If it is not given then I would use a Lagrangian approach.
 
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I think it can be done in Newtonian mechanics since the problem states that the acceleration of the plane (and i hope it doesn't mean the acceleration of the c.o.m only) is only in the +y direction. Of course this means there is some sort of constraint that prevents the rotation of the plane around its c.o.m (like that the plane is moving between two vertical walls).
 
bongobl said:
Hi guys I am trying too find a formula to figure out how I would find the acceleration of a block on an incline plane IF that plane itself were accelerating in the +Y direction.
Such as if the incline were fixed to the floor of an accelerating elevator? (The simplest case.)

If so, I would use the accelerating frame of the incline, being sure to add the appropriate inertial pseudo force due to the acceleration. (Of course, you have several options.)
 
If the inclined plane is accelerating upwards at a rate of "u" m/s^2, then let g' = g (gravitational acceleration) + u (inclined plane upwards acceleration). Solve as if the plane was not accelerating, using g' instead of g, then when completed, add the block's acceleration vector with respect to the incline plane and the upwards acceleration of the inclined plane with respect to the groung to get the total acceleration vector with respect to the ground.
 

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