Physics Help Forum What is the true explanation for this?

 Kinematics and Dynamics Kinematics and Dynamics Physics Help Forum

 Feb 18th 2010, 05:45 AM #1 Junior Member   Join Date: Feb 2010 Posts: 1 What is the true explanation for this? hello people , I can't understand deduction of thrust force by this way? This is an extract from my book http://img693.imageshack.us/img693/3506/… well i have an explanation but not sure about it thrust exerts a force on the rocket , the rocket answers by a force equal in magnitude and opposite in direction which makes the rocket accelerate upwards since there is no external force affecting the system (because the system is isolated) therefore the net force affecting the system is zero (the sum of thrust force and rocket's reaction on thrust = 0) therefore F=d(mv)/dt=0 where F is the net force acting on the system by using the product rule we get : F= mdV/d t+ Vdm/dt=0 Therefore mdV/dt =- Vdm/dt = Fimp Where the negative sign indicates the direction so, Right?? If yes then write "right" if no say why? I have also another question what does each of mdV/dt and -Vdm/dt indicate??? does mdV/dt indicates the reaction of the rocket upwards and -Vdm/dt indicate the thrust on rocket??? Thanks

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