• Support PF! Buy your school textbooks, materials and every day products Here!

Speed of water and height involving fluid mechanics

  • #1

Homework Statement



In a very large closed tank, the absolute pressure of the air above the water is 6.01x10^5 Pa. The water leaves the bottom of the tank through a nozzle that is directed straight upward. The opening of the nozzle is 4.00m below the surface of the water. a) Find the speed at which the water leaves the nozzle. b) Ignoring air resistance and viscous effects, determine the height to which the water rises.

Thanks!

Homework Equations



P+rhov^2/2+rhogh= constant

P2=P1+rhogh

kinematics?


The Attempt at a Solution



I know that I can set the initial height to zero, but that's about it. I really don't know how to treat this problem.
 

Answers and Replies

  • #2
134
0
Use energy conservation to get velocity(u) of water just outside nozzle.You will get u=sqrt(2gs). Assuming nozzle is very small.Here s is distance of nozzle from topmost layer of water(4.00m). After getting velocity use kinematic equation (v^2)=(u^2)-2gh.
For highest point v=0.Thus getting h=u^2/2g.
Which is same as s(4.00m) as it should be from energy conservation(similar to ball thrown in air and returning back to earth and again reaching same height h after colliding from ground(assuming it to be elastic collision).
 
  • #3
Use energy conservation to get velocity(u) of water just outside nozzle.You will get u=sqrt(2gs).
Can you show me what the entire (energy conservation) equation is before you simplified it?
Is it Bernoulli's equation?

thanks
 
  • #4
134
0
Just take a small element of water of mass dm at a height s above the nozzle.
Initial energy=Potential Energy=dm*g*h
Final energy after just coming out from nozzle(assuming it to be at height 0)=0.5*dm*u^2
Equating final and initial energy you can get u=sqrt(2gs).
Here however we assume that nozzle is very small and let's only point particles out.Only then we can do mechanical energy conservation.
 
  • #5
134
0
Can you tell me that what would you do if nozzle is not very small, i.e. it has a small area 'a' and lets finite amount of water out(not point sized particles)??You also know area of topmost layer of water as 'A'.
Think it yourself.The answer becomes more interesting.
Hint:In that case don't apply energy conservation.You will apply only equations of fluids-->
Bernoulli and Equation of continuity.
 

Related Threads for: Speed of water and height involving fluid mechanics

  • Last Post
Replies
2
Views
660
Replies
4
Views
3K
Replies
4
Views
318
Replies
2
Views
959
  • Last Post
Replies
1
Views
488
  • Last Post
Replies
2
Views
4K
  • Last Post
Replies
9
Views
6K
Top