In a wheel and axle mechanism the diameters of the wheel and axle are 40cm and 8cm respectively. Given that the machine is 80% efficient, what effort is required to lift a load of 100N?
A
20N
B
25N
C
50N
D
80N
Verified Correct Answer: B.
Physical Principles & Numerical Solution
Efficiency = \(\frac{\text{work done by hand}}{\text{work done by effort}}\)
80 = \(\frac{100{\times 8}}{E {\times} 40}\) x \(\frac{100}{1}\)
E = 25N
Source: Myschool Past Questions Archive (Record #27605)