Two wooden crates rest on top of one another. The smaller top crate has a mass of m1 = 22 kg and the larger bottom crate has a mass of m2 = 94 kg. There is NO friction between the crate and the floor, but the coefficient of static friction between the two crates is μs = 0.75 and the coefficient of kinetic friction between the two crates is μk = 0.6. A massless rope is attached to the lower crate to pull it horizontally to the right (which should be considered the positive direction for this problem). The rope is pulled with a tension T = 239 N (which is small enough that the top crate will not slide).
What is the frictional force the lower crate exerts on the upper crate?
The Attempt at a Solution
if F(net)=T, then ma=T, and (94+21)a=239, a=2.08m/s2.
I really am not sure how to proceed from here to find the force of friction exerted by the lower block on the upper block....I would really appreciate some help! Thanks!