 Snow-collecting sled

A sled intercepting snow with zero horizontal velocity in the ground frame is a simple momentum flux example. At arrival rate $\sigma$, immediate removal with outgoing ground-frame horizontal velocity $v_{\mathrm{out}}$ gives $M\dot{v}=-\sigma v_{\mathrm{out}}$ for constant moving mass $M$. Removal sideways in the sled frame has $v_{\mathrm{out}}=v$ and exponential deceleration; removal sideways in the ground frame has $v_{\mathrm{out}}=0$ and constant sled velocity. Retained snow instead gives $(M+\sigma t)v=M{v}_0$. The outgoing reference frame must be specified.