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I am behind on taking the tests and I am trying to get caught up but I am have problems with some of the problems on the test and I need some help just getting them started and which equations I need to use for the problems.
Water is descending in a vertical pipe of diameter 7 cm and open to the atmosphere. At a lower point the water flows into a smaller pipe of diameter .90 cm. At a certain instant the depth of the water just above the narrowing point is 80 cm and the water is moving at 150 cm/s. What is the gauge pressure of the water just above the narrowing point? What is the pressure change across the narrowing point? This is one problem and for some reason I am stuck on how to start the problem. I know that you have to use the 80cm and 150cm/s to find the pressure before the narrowing point. Will that be the gauge pressure? How would find the change in pressure?
The ratio of water velocities before and after the narrowing is the reciprocal of the ratio of cross-sectional areas before and after the opening.
Bernoulli's Equation applies to this situation. Altitude difference is not important, so it's the change in the velocity term that gives rise to the pressure difference.
The problem as stated here doesn't have enough information to calculate the gauge pressure. If you knew how much water there was above the narrowing point then you would be able use the change in altitude between the surface and that point to find the gauge pressure. Gauge pressure is not absolute pressure, but absolute pressure minus atmospheric pressure.
If you have the density of a material and you submerge it in water how do you find the tension in the string that is holding the material in the water? do you need to find the specfic weight of the material to find the tension?
The buoyant force is equal to the weight of the water displaced. The gravitational force on the sample is the mass of the sample multiplied by the acceleration of gravity. The mass of the sample is equal to its density times its volume.
The only forces acting are the buoyant force, the weight of the object and the tension is zero. The net resultant of these forces is zero, since the object is in equilibrium.
If you have the volume and the density of the sample, or if you have information that allows you to find these quantities, then you can solve the problem.
Will you write down all of the equations that we should know for the first test so I can see if I have all of them and so I can try some more problems before I try to take the test.
If you give me a list of equations and concepts as you see them, I'll be glad to comment and mention the things that appear to be missing.
Thanks I hope I can catch up soon and get back on track.