Find Magnitude of Total Contact Force on 20kg Box in 3 Cases

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    Friction Mechanics
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Discussion Overview

The discussion revolves around calculating the magnitude of the total contact force on a 20 kg box at rest on a rough horizontal surface under three different applied force scenarios. Participants explore the implications of different force applications and their effects on the normal force exerted by the surface.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants calculate the total contact force for case (a) as 204N, while others suggest it should be 196N based on the weight of the box.
  • In case (b), one participant arrives at 213N, while the textbook states 193N, leading to uncertainty about the correct interpretation of the applied forces.
  • For case (c), calculations yield 187N from one participant, contrasting with the textbook's 218N, indicating a potential misunderstanding of the vertical components of the applied forces.
  • One participant questions the definition of total contact force, interpreting it as the normal reaction force, and seeks clarification on how the textbook defines it.
  • Another participant suggests that free body diagrams may aid in understanding the forces involved in each scenario.

Areas of Agreement / Disagreement

Participants express differing views on the calculations of the total contact force, with no consensus reached on the correct values or interpretations of the applied forces. Multiple competing views remain regarding the definitions and calculations involved.

Contextual Notes

Participants have not provided all assumptions or definitions used in their calculations, leading to potential discrepancies in interpretations. The discussion lacks clarity on the specific definitions of total contact force and how vertical components of applied forces are accounted for.

Shah 72
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A box of mass 20 kg is at rest on a rough horizontal ground. Find the magnitude of the total contact force in each of the cases.
a) The box is pulled horizontally to the right by a force of 40N
b) the box is pushed to the left by a force of 50N at 15 degree above the horizontal .
c) the box is pushed to the left by a force of 50N at 15 degree below the horizontal.
 
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Shah 72 said:
A box of mass 20 kg is at rest on a rough horizontal ground. Find the magnitude of the total contact force in each of the cases.
a) The box is pulled horizontally to the right by a force of 40N
b) the box is pushed to the left by a force of 50N at 15 degree above the horizontal .
c) the box is pushed to the left by a force of 50N at 15 degree below the horizontal.
I have worked out the ans for a) will be 204N.
b) iam getting the ans 213N, but the textbook says 193N
c) I get the ans 187N , the textbook ans is 218N.
 
Shah 72 said:
A box of mass 20 kg is at rest on a rough horizontal ground. Find the magnitude of the total contact force in each of the cases.
a) The box is pulled horizontally to the right by a force of 40N
b) the box is pushed to the left by a force of 50N at 15 degree above the horizontal .
c) the box is pushed to the left by a force of 50N at 15 degree below the horizontal.
I have worked out the ans for a) will be 204N.
b) iam getting the ans 213N, but the textbook says 193N
c) I get the ans 187N , the textbook ans is 218N.

I don't get any of those values, yours or the text. I'm interpreting total contact force as the Normal Reaction Force the rough (assumedly horizontal) surface exerts upward on the box. Is that how your text defines it?

Is there more information that you haven't posted?
 
skeeter said:
I don't get any of those values, yours or the text. I'm interpreting total contact force as the Normal Reaction Force the rough (assumedly horizontal) surface exerts upward on the box. Is that how your text defines it?

Is there more information that you haven't posted?
The question is Q(3)
20210420_100046.jpg

This is the exact info in the textbook. And iam getting a different ans from the ans given in the textbook.
20210420_100046.jpg
20210420_100046.jpg
 
(a) normal contact force = weight = 20g = 196 N

(b) normal contact force = weight - vertical component of the applied force = 20g - 50sin(15) = 183 N

(c) normal contact force = weight + vertical component of the applied force = 20g + 50sin(15) = 209 N

may help your understanding if you sketched free body diagrams for each situation
 

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