Why Is My Coefficient of Friction Negative?

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Homework Statement

I just did a lab at school dealing with coefficient of friction for an object on an incline. After all my calculations done, my answer is negative for a cart sliding down, dealing with kinetic friction.

Homework Equations

The Attempt at a Solution

I have checked all my calculations and have found nothing wrong.

 

[PhanthomJay]

Well how can we help unless you show us your calcs??

 

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My question is whether the coefficient of friction can be negative?

 

[PhanthomJay]

Oh, no.

 

[TVP45]

Did you turn the ramp around so the angle was in the 2nd quadrant?