F.4 phy about force and mption~~

如果只係當CE題目的話, 咁樣下面位兄弟就答啱啦, 但係如果我地係睇現實生活的話, 咁就重有好多野要補充.

首先就係機翼的角度, 因為機翼唔會係水平的, 所以個lifting force (即係你口中的F) 係會同機翼的角度有關的, 我想你也會知force 係要拆components 的.

其次就是就uniform velocity, 因為現實生活入面, 我地係唔可以neglect air resistance 架, 而個air resistance 就正正同個velocity 成正比, 即係velocity faster, air resistance faster, 所以呢, 如果真係要計, 咁就起碼要用second order 的 ordinary differential equation 來計啦.

就算我當個engine power output constant, air resistance constant, 但係係大自然入面都會有好多突發事情, 好似係風吹雨打咁, 所以係好難keep 一個constant velocity.

我呢一個答案係從別一個方向出發, 可能未必答到你個問題, 但係就肯定可以比到多d information 你reference

If the force F is acting normally to each wing, then 2F are acting against the self weight of the aeroplane, i.e. mg where g is the gravitational acceleration. Therefore,
2F = mg

The plane will continue to fly in uniform velocity as long as there is no external force exerted on the plane horizontally.