Solving Friction Homework: F=ma, Fk=u*Fn

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SUMMARY

The discussion focuses on solving a physics homework problem involving friction and Newton's second law, specifically using the equations F = ma and Fk = u * Fn. The initial calculations incorrectly assumed a side view, leading to an erroneous acceleration of 7.1 m/s². After clarifying the perspective as an overhead view, the correct resultant force was calculated as 22 N, resulting in a net force of 18 N and a corrected acceleration of 9 m/s². The importance of accurately interpreting the problem's diagram is emphasized for correct solutions.

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Homework Statement


screenshot_25.png


Homework Equations


F = ma
Fk= u * Fn

The Attempt at a Solution


By analyzing the forces into components and applying Newton's second law

Fnet on y-axis = 0
So, Fn = mg + F2sin37 - F1sin 37 = 20 + 9 = 29 N

on x-axis
F = ma
F1 cos 37 + F2 cos 37 - Ffr = ma
F1 cos 37 + F2 cos 37 - uK * Fn = ma
5*0.8 + 20*0.8 - 0.2*29 = 2a
4 + 16 - 5.8 = 2a
14.2 = 2a
a = 7.1 m/s2Can you guide me to know my mistake, please?

Thanks in adavance
 
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Looks like you assumed the figure depicts a side view. Maybe it's an overhead view. If so, I think you should get one of the answers listed.
 
So I find the resultant force which is:
25*0.8 - 15*0.6 = 20 i - 9j
Magnitude = 21.9 ~= 22 N

Friction force is 0.2 * 20 = 4 N

Net force = 22 - 4 = 18 N

F = ma
18 = 2a
a = 9 m/s2

thanks!
 
Looks good!
 

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