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Let's say that we have a thruster whose exhaust velocity is very close to the speed of light. So when we calculate the mass flow rate to calculate the thrust do we take into consideration the relativistic mass of the exhaust ?

I think we should consider the relativistic mass of the exhaust and not the rest mass of the exhaust while calculation of the mass flow rate.

Am I correct ? Sorry If this is a newbie question as I know very little about relativistic mechanics.

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    $\begingroup$ You could, but it's better to just avoid relativistic mass and think about this in terms of relativistic momentum. See why we generally avoid relativistic mass here: physics.stackexchange.com/q/133376/123208 $\endgroup$
    – PM 2Ring
    Commented yesterday
  • $\begingroup$ Ok thanks. But the resultant thrust at relativistic speeds would be Lorentz factor times larger right ? $\endgroup$
    – Kshitij_Jha_7
    Commented yesterday
  • $\begingroup$ Right. But don't think of that Lorentz factor being somehow "bound" to the mass. Instead, see it as a component of the momentum equation, $p = mv\gamma$ $\endgroup$
    – PM 2Ring
    Commented yesterday
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    $\begingroup$ Thanks ! Got it. $\endgroup$
    – Kshitij_Jha_7
    Commented yesterday

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