Positive SSL
1 螺旋起重機,手柄半徑為R,螺紋導程為L,設摩擦不計,則其機械利益約為
A πR/L
B 2πR/L
C L/πR
D L/2πR

W=W

F × 2πR = W × L

M = W/F = 2πR/L