hello people
This is an extract from my book about my problem
http://img693.imageshack.us/img693/3506/thrustforce.jpg
I have an explanation for this but not sure about it :
Pushing the rocket with a high speed
when a great amount of
burnt gases are pushed backwards
with a great momentum , the rocket
gains the impulse forward with
an equal momentum (According to
the law of conservation of linear momentum).
Also thrust exerts a force
upon the rocket , the rocket answers in the opposite direction with a force equal in magnitude (According to Newton's third law).
F net = d(mV)/dt
and since both mass and velocity are changing from time to another:
therefore :
d(mV)/dt = mdV/dt + Vdm/dt (According to the product rule where the formula of the product rule is(f.g)'=f '.g + f.g' or
d(u.x)/dy = xdu/dy + udx/dy )
And since this system (rocket and thrust) is an isolated system (which means that no external force acting on the system ) therefore the linear momentum is conserved and the the change in momentum is zero , consequently the net fore is zero .
therefore F net = mdV/dt + Vdm/dt = zero
where F net is the net force on the system .
therefore : mdV/dt = - Vdm/dt = Fimp
where Fimp is the thrust force which is a self generated force and is directly proportional to the rate of emission of exhaust or the rate of decrease of mass of the gases
m ----- indicates the mass of rocket plus the remainig fuel ,
dV/dt ------indicates the acceleration of rocket plus the acceleration of exhaust,
-V-------indicates the velocity of exhaust with respect to the rocket,
dm/dt-----indicates the rate of emission of thrust .
so is my explanation right???Thanks
