Calculate the coefficint of kinetic friction between the slide and the child

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Homework Statement


A child slides down a slide with a 28 degree incline, and at the bottom her speed is precisely half of what it would had been if the slide had been frictionless. Calculate the coefficint of kinetic friction between the slide and the child.


Homework Equations



N= -mgcos =0
Fy= mgsin =ma

N= -mgcos(28)
-Fy + f = ma

mgsin(28) + Mu mgcos(28) = ma


The Attempt at a Solution



I have no attempt all my answers seem to be coming out wrong the books answer is .4 but the closest i can get is .53. I found acceleration but that didnt help much. I honestly lost on this problem. If you can please help me Id appreciate if very much. Thank you
 
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Be careful with the signs of the forces. Which way does friction act? (You're on the right track.)
 
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