Why Is the Resultant Force on the Blade Directed Downwards?

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Homework Help Overview

The discussion revolves around understanding the direction of the resultant force acting on a blade in a fluid dynamics context. Participants are questioning why the resultant force is directed downwards towards point A, despite the presence of horizontal and vertical force components that suggest an upward resultant force.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants are analyzing the components of force acting on the blade, including horizontal and vertical forces. There are questions about the direction of the resultant force and whether it should be upwards based on the calculated components. Some participants point out potential errors in the force equations and discuss the implications of these errors on the resultant direction.

Discussion Status

The discussion is ongoing, with participants providing insights into the calculations and questioning the assumptions made regarding the forces acting on the blade. There is a focus on clarifying the relationship between the forces on the blade and the forces exerted by the stream of water, though no consensus has been reached on the direction of the resultant force.

Contextual Notes

Participants are working with specific force values and components, and there are indications of potential typos in the equations being referenced. The discussion includes the need to negate certain forces to determine the forces acting on the blade, which adds complexity to the analysis.

werson tan
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Homework Statement


why the resultant force on blade is acted downwards (toward A)? why shouldn't it be slanted upwards ?
since the horizontal component of the force acted 2.12kN to the left , and 0.735kN upwards , we would get the resultant force acting slanted upwards , right ?

Homework Equations

The Attempt at a Solution

 

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There is a typo in the Fx equation. The second 12cos60-12 should be 12cos60+12.
In the final answer, take note of the direction of the arrow. The angle is 19.11 degrees to the centreline (x axis). The "towards A" just means it is clockwise from that centreline.
 
haruspex said:
There is a typo in the Fx equation. The second 12cos60-12 should be 12cos60+12.
In the final answer, take note of the direction of the arrow. The angle is 19.11 degrees to the centreline (x axis). The "towards A" just means it is clockwise from that centreline.
the horizontal component of force should be -1.272 N + 2.54 = 1.27N N to the right, whereas the direction and magnitude of vertical force is the same ? then , the direction of resultant of force should be upwards just like the diagram below?
 

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werson tan said:
the horizontal component of force should be -1.272 N + 2.54 = 1.27N N to the right, whereas the direction and magnitude of vertical force is the same ? then , the direction of resultant of force should be upwards just like the diagram below?
The calculated Fx and Fy are forces on the stream of water. To get the forces on the blade you have to negate both, giving 2.12kN to the right and 0.735kN down.
 
haruspex said:
The calculated Fx and Fy are forces on the stream of water. To get the forces on the blade you have to negate both, giving 2.12kN to the right and 0.735kN down.
isnt that the the resultant force on blade and forecs of steam of water are of same magnitude and same direction
?
 
werson tan said:
isnt that the the resultant force on blade and forecs of steam of water are of same magnitude and same direction
?
Action and reaction are equal and opposite. The force the blade exerts on the stream of water is equal and opposite to the force the water exerts on the blade.
 
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