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Nick

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  1. I'd appreciate any answers to this logic conundrum. Thanks.  

    Engineers are confronted with two apparently true but contradictory statements: 

    a)    To fly, lift must equal the weight of the airplane (Lift = Weight). 

    b)    Commercial airliners such as Boeing 747-400 and Airbus 320 have thrust-to-weight ratios of about 0.3.  i.e.  Thrust / Weight  =   0.3

    If the engine thrust (Thrust) is 3N, then the weight must be 10 N, and the Lift must be 10 N as well. 

    But there is a significant problem: According to this logic, 10 N of Lift is 7 N greater than the 3 N of Thrust. This is impossible as 3 N of Thrust cannot produce the Lift of 10 N.  

    Hence a paradox arises, as equations (a) and (b) appear true when stated individually. But combined they produce equation (c) ‘Thrust / Lift = 0.3’ that is false (i.e. impossible).

    Therefore, one of the equations (a) or (b) must also be false.  But which one? 

     

    lift paradox.png

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