Stupid physics problem.

[Pat Fairbank]

I did the second problem and got the force of friction = 103.55 N, and mu = 0.67.

First, you find the weight of the box.
w=mg=(19)(9.8)=186.2 N

Then you find the parallel force and the normal force.
Fp=w*sin(angle)=186.2*sin(34)=104.12
Fn=w*cos(angle)=186.2*cos(34)=154.37

So by F=ma:
Fp - F(friction) = ma
104.12 - F(friction) = (19)(0.03)
F(friction)=103.55 N

Now we can solve for mu:
F(friction)=mu*Fn
103.55=mu*154.37
mu=0.67

Does this help at all?