Ff = N u
The Attempt at a Solution
Pretty much, I did the same thing in the solution.
For box A:
N = mg
Ffs = mg*uk = 9.81*20*.4=78.48N
I note that Ffs > 60 N, so the boxes will move with the same acceleration
Now there are two ways I can approach this problem, each gives me a different answer??
1) Take two boxes as the same system, then Fx = 70*a = 60 ==> a = 0.857 m/s^2
2) Look at the FBD of box 2, note that Fx = 50*a = 60 ==> a = 1.2 m/s^2
However, both of these answers are different than the solution.
Where did I mess up (and why do 1 &2 give different solutions?)