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Classical Physics
Mechanics
Newton's second law -- rockets
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[QUOTE="PeroK, post: 6866114, member: 493650"] Note that the "new form" of Newton's second law given here is not valid in general. There are several threads on here analysing this question. In fact it's not really Newton's second law, but an equation that is only valid in this specific case. PS the author has confusingly used the same letter ##v## for the velocity of the rocket and the velocity of the expellant. A simpler way to look at this is to use conservation of momentum: $$m_r\Delta v_r + \Delta m_e v_e = 0$$Where we need the assumption that ##\Delta m_e## is small compared to ##m_r##. Otherwise, we would need to be more explicit that the mass of the rocket is changing from ##m_r + m_e## to ##m_r## after the expellent is fired out. [/QUOTE]
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Newton's second law -- rockets
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