Newton s second law of motion
Net force = rate of change of momentum
Consider first a stationary tank into which solid masses are thrown, Figure (1- a). Momentum is a vector and each component can be considered separately; here only the x-component will be considered. Each mass has a velocity component v, and mass m so its x-component of momentum as it enters the tank is equal to mvx.
As a result of colliding with various parts of the tank and its contents, the added mass is brought to rest and loses the x-component of momentum equal to mvx .As a result there is an impulse on the tank, acting in the x-direction. Consider now a stream of masses, each of mass m and with a velocity component ?x.
If a steady state is achieved, the rate of destruction of momentum of the added masses must be equal to the rate at which momentum is added to the tank by their entering it. If n masses are added in time t, the rate of addition of mass is nm/t and the rate of addition of x-component momentum is (nm/t)?x. It is convenient to denote the rate of addition of mass by M, so the rate of addition of x-momentum is M?x.
Figure 1-b shows the corresponding process in which a jet of liquid flows into the tank. In this case, the rate of addition of mass M is simply the mass flow rate. If the x-component of the jet’s velocity is ?, then the rate of ‘flow’ of x-momentum into the tank is M?x. Note that the mass flow rate M is a scalar quantity and is therefore always positive. The momentum is a vector quantity by virtue of the fact that the velocity is a vector.
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
الرجوع الى لوحة التحكم
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