Extra work (overcoming the gravity of the lever itself, the work done by friction w extra =W always -W useful)
Total hours (w total =FS)
Pulley block: useful (w useful =Gh)
Extra work (work done to overcome the weight of moving pulleys, ropes and friction)
①W Extra = W Total-W used
(2) If the rope weight and friction force are not considered, W extra =G moves H)
Total hours (w total =FS)
Inclined surface: useful work (w useful =Gh)
Extra work (work to overcome friction)
①W Extra = W Total-W used
② WEEXTRA = FL) Note: F refers to the friction force L refers to the length of the inclined plane.
Total work (W total =FL) Note F refers to the pulling force.
Calculation of mechanical efficiency
Lever: η=W Useful ÷W Total =Gh÷FS
Where g is the gravity of the lifted weight, h is the height of the weight, f is the strength, and s is the moving distance of the strength point.
Pulley or wheel set:
① Lifting heavy objects: 1, η=W Useful ÷W Total =Gh÷FS=G÷nF
2. Regardless of the rope weight, the friction η=Gh÷(Gh+G moving h)=G÷(G+G moving).
② Horizontal uniform pulling: η=W Useful ÷W Total =fs object ÷Fs rope =f÷nF.
Inclined plane: ①η=W Useful ÷W Total =Gh÷FL
②η= Gh \u( Gh+fL)
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This is all within the scope of grade three.