Understanding Friction: Solving for Forces on Boxes A and B

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SUMMARY

The discussion focuses on the mechanics of two boxes, A and B, under the influence of friction and applied forces. It is established that an applied force of 18N on box A is the minimum required to overcome static friction, leading to the conclusion that box A is on the verge of movement. Additionally, box B experiences two horizontal forces: the kinetic friction from box A and the static friction with the ground, which are essential for calculating its motion using the equation F = ma.

PREREQUISITES
  • Understanding of Newton's Second Law (F = ma)
  • Knowledge of static and kinetic friction coefficients
  • Familiarity with free body diagrams
  • Basic principles of mechanics involving forces and motion
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  • Study the concepts of static and kinetic friction in detail
  • Learn how to construct and analyze free body diagrams for multiple objects
  • Explore the application of Newton's laws in real-world scenarios
  • Investigate the effects of different friction coefficients on motion
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Students studying physics, particularly those focusing on mechanics, as well as educators and anyone interested in understanding the principles of friction and force interactions in systems involving multiple objects.

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Homework Statement



[PLAIN]http://img510.imageshack.us/img510/3893/58096739.jpg

Homework Equations



F = ma, friction...

The Attempt at a Solution


I just want to understand the problem so I can do it.

1a. If I apply 18N to box A, does it actually move? or it just reaches the max friction and still stay put?

1b. how many forces should be on box B? I see 2 forces, the kinetic friction given by A on B and the static (or kinetic?) friction between box B and the ground
 
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Hi Iva! :smile:
IvaNMK said:
1a. If I apply 18N to box A, does it actually move? or it just reaches the max friction and still stay put?

The 18 N applied force in the question is stated to be the minimum force needed to get box A to move (ie, "to overcome the maximum static friction").

There's two answers to your question! …
i] no, it's only "on the point of moving" or "about to move", to quote various exam questions on static friction
ii] yes, it moves imperceptibly slowly at first, but then the coefficient of kinetic friction takes over, so it accelerates. :wink:

1b. how many forces should be on box B? I see 2 forces, the kinetic friction given by A on B and the static (or kinetic?) friction between box B and the ground

Yes, only 2 (horizontal) forces on B …

their total is the F in F = ma for B. :smile:
 

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