Fluid mechanics - is there enough information for this problem?

In summary, the student is frustrated with the TA for leaving out important information in homework assignments. They are struggling with a problem involving the conservation of linear momentum and mass flow, and are unsure how to find the velocity without given densities. They suggest using equations for the sum of forces in the x and y directions and conservation of mass flow, but are still unsure how to proceed without the necessary information.
  • #1
pyroknife
613
4
Attached the problem.

The TA for my class makes up all the damn homework problems, but she has a habit of leaving out important information on every single homework assignment. Sorry for the rant, just had to vent a bit.

Unless they want all this in variables, I don't see a way to get a # for the velocity. We're not given any densities...am i supposed to assume that the density for both inlets are the same?
Cross section for the exit is not given...my approach was to use the conservation of linear momentum
as stated in the problem, the horizontal and vertical forces are 0.

m'=mass flow (kg/s)
m'1=mass flow at inlet 1
m'2=mass flow at inlet 2
m'3=mass flow at outlet 3
V1=velocity1
Sum of forces in the x gives: m'1*V1=(m'1+m'2)*V3*cos(theta)
sum of forces in the y gives: m'2*V2=(m'1+m'2)*V3*sin(theta) << solving this equation for V3 and substituting back into other equation gives
m'1*V1=m'2*V2*cos(theta)/sin(theta)

That's 3 unknowns

I guess I can do CONSERVATION of mass flow as well

m'1+m'2=m'3
density1*Area1*velocity1+density2*area2*velocity2=density3*area*3*velocity*3
This doesn't really help me at all.
 

Attachments

  • Untitled.png
    Untitled.png
    23.9 KB · Views: 377
Last edited:
Physics news on Phys.org
  • #2
Assuming the densities are the same, separately equate the forces in the x and y directions. For instance:

Q1 * V1 = Q3 * V3 * cos(theta)

where Q = V * A

so

A1 * V1^2 = A3 * V3^2 * cos(theta)

etc...
 

FAQ: Fluid mechanics - is there enough information for this problem?

1. What is fluid mechanics?

Fluid mechanics is a branch of physics that deals with the study of fluids, which includes liquids, gases, and plasmas. It involves the analysis of how fluids behave under various conditions, such as flow, pressure, and temperature.

2. How does fluid mechanics relate to real-world problems?

Fluid mechanics is essential in understanding and solving many real-world problems, such as predicting weather patterns, designing airplanes and ships, and developing medical devices. It also plays a crucial role in various industries, including aerospace, automotive, and energy.

3. What are the key principles of fluid mechanics?

The key principles of fluid mechanics include continuity, conservation of mass, conservation of energy, and conservation of momentum. These principles help to explain how fluids behave and interact with their surroundings.

4. Is there enough information for this problem?

This question is difficult to answer without knowing the specific problem in question. Generally, fluid mechanics problems require specific equations and data to be solved accurately. It is essential to have enough information and data to accurately model and analyze the problem.

5. How can I apply fluid mechanics concepts in my daily life?

Fluid mechanics has many practical applications in our daily lives. For example, understanding the principles of fluid pressure can help us operate simple machines, such as bicycle pumps. Additionally, knowledge of fluid dynamics can help us understand weather patterns and how to design more efficient cars and airplanes.

Similar threads

Replies
4
Views
1K
Replies
1
Views
3K
Replies
10
Views
4K
Replies
6
Views
1K
Replies
8
Views
17K
Replies
2
Views
2K
Back
Top