Confusion regarding the concept of acceleration along a component

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Discussion Overview

The discussion revolves around the concept of acceleration in a system involving a wedge and a block. Participants explore the conditions under which the block remains stationary on the inclined plane of the wedge while the wedge itself is being pushed. The focus is on understanding the implications of negative acceleration and the forces acting on the block and wedge.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant suggests that if the acceleration of the wedge is A, then the acceleration of the block along the incline can be expressed as gsinθ + Acosθ = 0, implying A is negative.
  • Another participant clarifies that A being negative is relative to the block, as the block tends to slide down the wedge when a force is applied, indicating an opposite acceleration direction.
  • A later reply questions the physical possibility of applying a force while experiencing negative acceleration, suggesting potential inconsistencies in the choice of positive direction or the forces considered.
  • One participant states they have taken the x-axis parallel to the incline of the wedge, which they believe is relevant to the discussion of forces and accelerations.
  • Another participant emphasizes that the components of acceleration (Acosθ and -gsinθ) are in opposite directions, leading to the conclusion that their resultant must be zero.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of acceleration and forces in the system. There is no consensus on the physical implications of negative acceleration or the correctness of the applied forces.

Contextual Notes

Participants have not fully resolved the assumptions regarding the direction of forces and accelerations, nor have they clarified the conventions used for positive and negative directions in their calculations.

AakashPandita
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Suppose we have a wedge with angle θ on which there is a block. We are pushing the wedge with the least force required to keep the block stationary. If the acceleration of wedge is A then the acceleration of the block along the inclined plane will be gsinθ+Acosθ=0. That means A is negative.

How is this possible physically that we apply a force and the body is accelerating negatively in that direction?
 
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A is negative, relative to the block ( as you are calculating the acceleration of the block). As you apply the force on the wedge, the block tends to slide down,(as far as I have inferred, the sloping surface of the wedge faces the source of force) which means it accelerates in the opposite direction. Or, standing on the block, you can say the wedge is accelerating in the direction opposite to the block.
 
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thank you for replying. please reread my post. i edited it. made my question more clear.
 
AakashPandita said:
How is this possible physically that we apply a force and the body is accelerating negatively in that direction?

It's not. You've either
1) been inconsistent in your convention for deciding which is the positive direction: left to right or right to left. Are you seeing the wedge accelerating right to left, while your x-axis has increasing values of x to the right? If so, both the force and the acceleration are negative (in the direction of decreasing x).
2) used the force that the block exerts on the plane, when you should have used the equal and opposite force that the plane exerts on the block.
 
i have taken the x-axis parallel to the incline of the wedge.
 
AakashPandita said:
thank you for replying. please reread my post. i edited it. made my question more clear.
AakashPandita said:
We are pushing the wedge with the least force required to keep the block stationary.
Yeah. I had considered that.
AakashPandita said:
i have taken the x-axis parallel to the incline of the wedge.
O K then...Check the equation again. Acosθ and gsinθ are in opposite direction. If one is towards the positive X-Axis direction then the other is in the negative.
The resultant acceleration must be zero.
That is,
Acosθ+(-gsinθ)=0
Acosθ=gsinθ
 
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