Question

If a `8 kg` object moving at `18 m/s` slows to a halt after moving `180 m`, what is the coefficient of kinetic friction of the surface that the object was moving over?

Answer 1

k=0.0917

Explanation:

`m:` mass of object
`g=9,81`
`G=m.g=8 . 9,81=78,48 N` "Gravity of object"
`N=-G=-78,48 N` "reaction to object by surface"
`F=k.N=-k.78,48 N`" friction force between surface and object"

`step 1:`

Object have lost the kinetic energy between the Point A and B.
`Delta E_k=1/2 m(0^2-18^2)`
`Delta E_k=1/2 8 (0+324)`
`Delta E_k=4* 324=1296` Joule

`step 2:`
`W:` work doing by friction force
`Delta E_k=W`
`1296=F * Deltax`
`Delta x=180 meters`
`1296=k*78,48*180`
`1296=k*14126,4`
`k=0.0917` "has no unit"