Two blocks of mass m1 = 15 kg. and m2 = 9 kg. are pushed against each other (m1 on top) and sliding down an incline of 35 degrees.

a) If the plane is frictionless, what is the normal force between the two masses?

b) If the coefficient of kinetic fricton between m1 and the plane is mu1 = 0.25, and between m2 and the plane is mu2 = 0.25, what is the normal force between the two masses?

c) If mu1 = 0.15 and mu2 = 0.25. What then would the normal force be?