FRICTION$-$APPLIED PROBLEM

Each crate on the sloping chute in Fig. $1$ weight $39[$Lb$].$ The coefficient of static friction $=0\mathrm{.}3.$ A spring$-$loaded roller at B applies a constant force of $54[$Lb$].$ Determine the maximum number of crates that can be held on the chute before the bottom crate is pushed by the top crates onto the rollers at $A.$

Fig.$-1$

Solution: