= Jet-area adjustment during ballistic slowing
{title2=$A_{\rm hit}v_{\rm hit}=A_0u_0$}
Steady incompressible <mass flow rate> stays constant along a jet, while speed and cross-sectional area can change under gravity. At a horizontal apex the arriving speed is the initial horizontal component. The force on a target that stops this horizontal momentum is $\dot m v_{\rm hit}$, using the conserved nozzle mass flux. Substituting the nozzle area into $\rho A_{\rm hit}v_{\rm hit}^2$ without adjusting the area gives the wrong result.
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