physics
posted by janie .
You push a box along the floor against a constant force of friction. When you push with a horizontal force of 75 N the acceleration of the box is 0.55 m/s2; when you increase the force to 85 N the acceleration is 0.78 m/s2.
(a) Find the mass of the box. kg
(b) Find the coefficient of kinetic friction between the box and the floor.

Net force= m*a
75friction=m*.55
85friction=m*.78
subtract the first equation from the second
10=m(.23)
m= 10/.23
then solve for friction in either equation, finally, mu=frictionforce/mg 
thank you