6-31 A horizontal water jet impinges normally upon a vertical plate which is held on a frictionless track and
is initially stationary. The initial acceleration of the plate, the time it takes to reach a certain velocity, and
the velocity at a given time are to be determined.
Assumptions 1 The flow is steady and incompressible. 2 The water always splatters in the plane of the
retreating plate. 3 The water jet is exposed to the atmosphere, and thus the pressure of the water jet and the splattered water is the atmospheric pressure which is disregarded since it acts on all surfaces. 4 The tract is nearly frictionless, and thus fiction during motion is negligible. 5 The motions of the water jet and the cart are horizontal. 6 The velocity of the jet relative to the plate remains constant, Vr = Vjet = V. 7 Jet flow is nearly uniform and thus the effect of the momentum-flux correction factor is negligible, β ≅ 1.