The expression for the frictional force between the sled and the ground is:
[tex]F=k m g[/tex]
where [tex]k[/tex] is the coefficient of friction, m is the mass of the object and [tex]g=9.81 m/s^2[/tex] is the gravitational acceleration.
The friction force in our problem is F=80.85 N. The mass of the object is m=15 kg. Re-arranging the formula, we can find the value of k:
[tex]k= \frac{F}{mg}= \frac{80.85 N}{(15 kg)(9.81 m/s^2)}=0.55 [/tex]
