Solved Exam Problem: Conservation Linear Momentum

MEC516/BME516 Fluid Mechanics I, Chapter 3: This is a sample solved problem from Fluid Mechanics Final Exam (2015). The problem requires the calculation of the force needed to hold a water jet nozzle in place using the conservation of linear momentum

All of the course videos and a copy (pdf) of this fluid mechanics presentation can be downloaded at:

Course Textbook: F.M. White and H. Xue, Fluid Mechanics, 9th Edition, McGraw-Hill, New York, 2021.

#fluidmechanics #fluiddynamics

[PeymanSayyadi]

Thanks for sharing these videos. I work in the industry and I wish the students know how useful it is to master these concepts.

[amaurybetancourt]

Thank you for these fantastic videos! Is there an additional vertical component of force (upwards) due to the torque about the left edge of the flange? I was thinking that, in addition to the momentum balance, a moment balance would show that the horizontal component of the discharge (to the right) creates a torque about the left edge (hinge) of the flange, which acts to lift and pivot the nozzle about the left edge. Perhaps this was already accounted for when you solved for the x-component of force, but if you could clarify, that would be helpful. Thank you!

[mrsengineering]

Peace be upon you sir... I need the name of the source for the Fluid Mechanics book and the number of copies. Thank you

[jondory]

Nice job... Related to the FBD, do you need to include a Moment, M, along with the Fx & Fy? (assume a direction...?)

[katlegophiri]

Hey! Just a few questions, hope you can help. Dont we use the sum of forces acting on the fluid = change in momentum and not the sum of the fluid acting on the nozzle or bend? Why was the force acting on the bend due to water changing direction not included?

[Ensign_Cthulhu]

Wait. If the force on the flange is in the negative Y direction, and that is DOWN, then the flange is under _compression_ onto its partner, in which case the pressure is holding the joint shut and the bolts can't be under tension.

A more advanced answer would require you to find the centres of gravity of the nozzle and the water within to make sure they weren't causing a tipping force on the bolts on the outer part of the curve.

[beholdayman]

why the different notations for x components and y components, those components being F(y) = m(v2 - v1) and F(x) = m(x2 - x1)

[SakeKaama]

Why is the momentum force in the opposite direction as the pressure force? Seems like they would both be acting in the same direction, no?

[DhushanSuresh]

SIR, IN THE QUESTION, ATMOSPHEARIC PRESSURE GIVEN AS 100 KPA SO HOW CAN YOU TAKE P2 GAUGE = 0?

[pavandevang]

sir can u please explain me how to take the direction of force

[mrsengineering]

Pleas sir I want this book pdf for fluid mechaincs