- #1

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## Homework Statement

## Homework Equations

F=ma

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?)