Kinetic/ Static friction- Newtons 3rd Law

AI Thread Summary
The discussion centers on a physics problem involving static and kinetic friction between two blocks. The coefficient of static friction is 0.60, while the kinetic friction coefficient is 0.20. Participants are trying to determine the least time required for both blocks to move 5.0 meters without the top block sliding. There is confusion regarding the role of static friction in the net force equations for both blocks, particularly how it affects the acceleration of the top block. Clarification is sought on how to incorporate static friction correctly into the calculations to solve for the required time.
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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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