Tough question about reaction force Newton's third law -- Please help

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SUMMARY

The discussion focuses on solving a physics problem related to Newton's third law and reaction forces. The correct answer to the question posed is 2f/5, derived from the equations F=ma and F=(5m)a. Participants emphasize the importance of correctly applying the mass of the second block and accounting for all forces acting on it to achieve the solution. The confusion arises from the distinction between the abstract force "F" and the specific force in the context of the problem.

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bomberkid
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Homework Statement


. question is as attached. answer is 2f/5..how do u get this?

Homework Equations


F=ma
F= (5m)a
a= F/(5m)

The Attempt at a Solution


gotten a=F/5m , but why the answer is 2f/5?
 

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What force is necessary to produce your calculated acceleration in the second block?
 
F?
 
No... you calculated the specific ##a##, now put that back into ##F=ma## along with the second block's mass

Unfortunately the confusion between the abstract "F" and the specific "F" in this problem is perhaps making understanding a little harder than it should be.
 
I see. Why not use the mass 3m?
 
bomberkid said:
I see. Why not use the mass 3m?
Either will do provided you bring all relevant forces acting on the mass into the equation.
 
but if i were to use f=3m, and a is F/5m, i wouldn't get 2f/5 as the answer
 
bomberkid said:
but if i were to use f=3m, and a is F/5m, i wouldn't get 2f/5 as the answer
You get the right answer if you bring in all forces acting on the mass and do the algebra correctly. Please post your working.
 

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