Force is equal to the mass flow rate times the change in velocity, the velocitys (in/out) are vector quantities.
For example: If the flow strikes the plate and turns 90 degrees, then the change in velocity is your 60 ft/sec, if it turns 180 degrees, then the change in velocity is 2 X the initial velocity.
The equation is dimensionally consistent in any rational system of units. If the units in the solution do not come out as a force, then your units are incorrect.