Horizontal force exerted by an engine

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Homework Help Overview

The discussion revolves around a problem involving the application of Bernoulli's equation and conservation of momentum to determine the horizontal force exerted by an engine. The original poster expresses confusion specifically about the second question in the homework, particularly regarding the calculation of velocity and density.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • The original poster attempts to use Bernoulli's equation to find the velocity at two points and apply conservation of momentum to find the force. They raise a concern about obtaining an imaginary number for velocity, questioning their approach.
  • Some participants suggest that there may be an error in the calculation of density, specifically regarding the value of the gas constant used in the equations.

Discussion Status

The discussion is ongoing, with participants exploring potential errors in the calculations and questioning assumptions about the constants used. There is no explicit consensus yet, but guidance has been offered regarding the specific gas constant.

Contextual Notes

Participants are discussing the implications of using the correct value for the gas constant in the context of the problem, which may affect the calculations and results. The original poster's confusion about the imaginary velocity suggests a need for further clarification on the setup of the problem.

theBEAST
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Homework Statement


I am only confused about question 2.
NSrLabC.png


The Attempt at a Solution


I decided to use bernoulli's equation to find velocity at point 1. With velocity at point 1 and point 2 I can use conservation of momentum to solve for the force exerted. In this case there would be Fx, pressure force at 1 and pressure force at 2. However as you can see in my second last and last lines of work, v1 comes out to be an imaginary number which is impossible.

What am I doing wrong?

8QPpLKw.jpg
 
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I think, in the step where you compute the density is wrong, 'cause R's value in the international system of measures is [tex]R=8,314 \dfrac{J}{mol \cdot K}[/tex]
 
Esteban said:
I think, in the step where you compute the density is wrong, 'cause R's value in the international system of measures is [tex]R=8,314 \dfrac{J}{mol \cdot K}[/tex]

The R in this equation refers to the specific gas constant of air, so it isn't 8.3146 I believe.
 
Oh, lol ahahahha
 

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