Respuesta :

Answer:

.5097

Explanation:

Original KE = 1/2 (100)(20)^2 = 20 000 J

the force of friction must work this hard to stop the object in 40 m

Ff  *40 = 20 000  

Ff = 500 =   Fn u         u = coeff of kinetic friction

       500 = (100)(9.81) u

           u = .5097