Two block on each other with friction

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    Block Friction
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Homework Help Overview

The discussion revolves around a physics problem involving two blocks stacked on each other, with a focus on the forces acting on them, particularly friction and normal forces. The subject area includes dynamics and frictional forces.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the calculations related to friction and normal forces, questioning the values used in the equations. There is an exploration of whether the normal force should be considered as the sum of the weights of both blocks or just one, and how this affects the frictional force.

Discussion Status

The discussion is ongoing, with participants providing feedback on each other's calculations and questioning the assumptions made regarding the normal force. There is no explicit consensus on the correctness of the original poster's solution, but guidance is being offered to clarify the relationships between the forces involved.

Contextual Notes

Participants are considering the implications of the normal force and friction in the context of the problem setup, including the potential for misinterpretation of the forces acting on the blocks.

Sarah00
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Homework Statement


screenshot_24.png


Homework Equations


F = ma
Ffr = u * Fn

The Attempt at a Solution


After drawing FBD
For m2: we have only friction force in horizontal axis so Ffr = ma ==> u * Fn = ma ==> u * mg = ma ==> u * g = a ==> a = 0.5 * 10 = 5 m/s2
Now, moving to m1:
F - Ffr = ma ==> F - u Fn = 10 * 5 ==> F - 0.5*130 = 50 ==> F - 65 = 50 ==> F = 115 N

But it is not in choices,

Is my solution wrong?
or
Are the choices wrong?
 
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One of the choices is right. Your solution is wrong.

a = Fnet/m

What mass is needed in this equation?
 
Sarah00 said:
Now, moving to m1:
F - Ffr = ma ==> F - u Fn = 10 * 5 ==> F - 0.5*130 = 50

Did you use the correct value for the normal force here?
 
I though that the mistake is with the Fn.
Fn here is the sum of two weights as net vertical force is zero

Dr Courtney, you considered them as single mass I see. The answer will be 65 N then. but I want to know my mistake
 
Sarah00 said:
I though that the mistake is with the Fn.
Fn here is the sum of two weights as net vertical force is zero

Think about whether the friction force acting on m1 is coming from m2 or coming from the ground.

What is the normal force acting between m1 and m2?
 

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