# Homework Help: Tank and a hole in it whats the speed?

1. Jun 10, 2009

### brunettegurl

tank and a hole in it whats the speed??

1. The problem statement, all variables and given/known data

A careless worker at a refinery accidentally punches a hole in a gasoline tank 47.4 m below the surface of the gasoline. The tank had been sealed under 3.07 atm of absolute pressure and the density of the liquid is 659 kg/m3.If the hole is 17.1 m above the ground and the pressure outside the tank is 1.00 atm, determine the speed at which the gasoline exits the hole.
2. Relevant equations

P1+ $$\rho$$gh+0.5*$$\rho$$V2=P2+$$\rho$$gh+o.5*$$\rho$$V2
3. The attempt at a solution
i tried to solve using the above question but i cant determine which number to use as height..pls. help

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2. Jun 10, 2009

### ideasrule

Re: tank and a hole in it whats the speed??

It doesn't matter what you use for the height; just pick a reference level--that is, a point where you define h to be 0--and stick with it. The reference level can be the ground, the hole, or even the top of the gasoline. It doesn't matter as long as you remember that h is negative for heights below the reference level.

3. Jun 10, 2009

### PhanthomJay

Re: tank and a hole in it whats the speed??

Something to ponder.....would you expect the exit speed of the gas to be different if the tank were punctured on the Rocky Mountains at elevation 5000 feet as opposed to being punctured on the Hawaiian Islands at elevation 0?

4. Jun 10, 2009

### brunettegurl

Re: tank and a hole in it whats the speed??

yes wouldnt the different atmosphere pressure effect the speed that it come out in??

5. Jun 10, 2009

### PhanthomJay

Re: tank and a hole in it whats the speed??

Yes, nice pondering. Also g would vary slightly. But what about the value of h to use? Do you agree with Ideasrules post?
Edit: I just noticed your equation does not include the use of subscripts for h1 and V1 on the left side of the = sign, and h2 and V2 on the right. I just want to be sure you are aware of that.

Last edited: Jun 10, 2009
6. Jun 10, 2009

### brunettegurl

Re: tank and a hole in it whats the speed??

my main problem is i dont know which value to use as my h1 and so on... i know i have to solve v2. i know my p1=3.07atm and p2=1atm...and if i just randomly choose a pt as h wont the answer change accordingly??

7. Jun 10, 2009

### PhanthomJay

Re: tank and a hole in it whats the speed??

No, as ideasrule point out, it won't matter. It's (h1-h2) that counts, which always comes out to the same value of 47.4 no matter what level of reference you use.

8. Jun 11, 2009

### brunettegurl

Re: tank and a hole in it whats the speed??

thanx that was my main problem..i got the answer