(续) 已知 W=70N
看图，求墙壁给予梯子的支持力  $F_{N1}$  
Refer diagram, determine the normal reaction force acted on the ladder by wall  $F_{N1}$   


(a)  

(续) 已知 W=70N,  $F_{N1}$  = 26.25 N
求地面给予梯子的摩擦力  $f$  
determine the friction exerted on ladder by ground  $f$  

(a)  

(续) 已知  $f$  =26.25 N,  $F_{N2}$  =70 N
求地面给予梯子的反作用力  $F_R$  
Determine the reaction force exerted on ladder by ground  $F_R$  

(a)  

(续)已知 $f$  =26.25 N,  $F_{N2}$  =70 N
问地面给予梯子的反作用力与水平呈多少度（°）?
How many degree(°) between the reaction force acted on the ladder by ground with the horizontal?
(填数字而已，不需单位)

(a)