Kinetic/ Static friction- Newtons 3rd Law

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SUMMARY

The discussion focuses on calculating the least amount of time required for two blocks to move a distance of 5.0 meters without the top block sliding off the lower block, given coefficients of static friction (0.60) and kinetic friction (0.20). The net force equations for both blocks are established, with the first block's equation being Fnet Box 1: T - (Fn x 0.6) = ma and the second block's equation as Fnet Box 2: T - (Fn x 0.2) = ma. The role of static friction in maintaining the top block's position is clarified, emphasizing that it acts in the positive direction to prevent sliding.

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  • Understanding of Newton's Laws of Motion
  • Familiarity with the concepts of static and kinetic friction
  • Ability to solve basic equations of motion
  • Knowledge of free body diagrams
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Homework Statement



The coefficient of static friction is 0.60 between the two blocks in figure. The coefficient of kinetic friction between the lower block and the floor is 0.20. Force causes both blocks to cross a distance of 5.0 m, starting from rest.
What is the least amount of time in which this motion can be completed without the top block sliding on the lower block?


Homework Equations




The Attempt at a Solution



Fnet Box 1: T-(Fn x 0.6)=ma

Fnet Box 2: T- (Fn x o.2)=ma

Where does static friction play into Fnet of box 2? I almost got it but the only way I could get the answer would be to have static friction in the positve direction. So it would be something like: Fs-Fk=ma . But I don't get how the static friction is in positive direction. please Help!
 
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T-(Fn x 0.6)=ma
What is the T?
It seems to me the only force acting on the top mass is Fn*0.6 so you can solve for the acceleration directly.
 

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