# Quick rocket question

1. Apr 11, 2005

wouldnt i just use this formula: $$v_f = v_i + v_{ex}*ln(m_i/m_f)$$
but i dont see how i would find the acceleration if there is no a. unless i solve for V_i, which is ..$$v_i = v_f - v_{ex}*ln(m_i/m_f) Dm/dt$$ and take the derivative? which should give me the acceleration right? a = -v_{ex}/m right?