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Holding nozzle stationary? (applications of COM, bernoulli's,mass flow

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Holding nozzle stationary? (applications of COM, bernoulli's,mass flow"

http://baen.tamu.edu/users/gilley/BAEN%20340%20Fluid%20Mechanics/Handout%20Items/Example%20Momentum%20Problem%20sets.pdf [Broken]

The problem is shown on page 12 of ^ link. It also shows the solutions. However the question asks could you hold the thing stationary. explain.

The answer is supposed to be yes.

They calculated the force to be about 159lb. This answer "yes" seems ambiguous. Why can the person hold the force stationary?

Does it depend on how much I weigh?
 
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Answers and Replies

  • #2
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They calculated the force to be 8344 N. That's about 1875 lbs. Obviously a person could not hold it but it certainly could be held by mechanical means.
 
  • #3
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No, the problem on page 12. They calculated it to be about 159lbs. If I weigh >159lbs, I can hold it stationary anything less and I can't. Is that how to interpret it?
 
  • #4
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Sorry, I was looking at the wrong problem. I and another person have held a fire hose of that size and about that pressure. It can be held by one person if he is a strong person but it takes large effort. You would not hold it for a long time so you'd better put the fire out fast. So, in general, my answer would be no.

The hose also has a tendency to whip. Since the load then is a moving one, the force can become greater than 159 pounds at times. When you consider friction between you and the ground, it would take more than one person to hold it.
 
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