minute 4:12 . Why do the rates for mp and mr have opposite signs? the rate at which the rocket loses mass,,,is it not the same rate at which the mass fuel variates?
papi chulo mp is not the same as the mass. mp is the exhaust velocity multiplied by the mass ejected during the time _t_; its momentum. As positive was defined to be to the right, mp is negative.
+Markus if we say the total mass is M = m_p + m_r, then (by conservation of mass/energy/momentum/etc) dM/dt must be 0. Therefore dm_p/dt and dm_r/dt must have opposite signs.
