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In a wheel and axle mechanism the diameters of the wheel ...

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

Correct answer is B

Efficiency = work done by handwork done by effort

80 = 100×8E×40 x 1001

E = 25N