TPR SCIENCE WORKBOOK PASSAGE 20 PHYSICS

[crazy person]

Does anyone know why the answer on #2 is C?

I thought the greater the pressure, the slower the velocity. Having said that, plug 3 has the greatest pressure, therefore it will have the slowest speed. Plug 1 has the lowest pressure, therefore the highest speed ? I don't see how plug 3 has the greatest speed ?
Can someone please explain this.

Thank you !!!!

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[butters221]

I don't have the workbook, but if you post the whole question I'll help you.

 

[dudewheresmymd]

This is just toricelli's law (conservation of energy)

top of tank=hole through tank
p1+pgh+1/2pv^2 = p2+pgh+1/2pv^2

p1=p2 ATM at both top of open tank and hole, cross both out
define h as 0 at the bottom, so cross out pgh on right side of equation
velocity at top of open tank is nearly 0 (assume rate of water flow at top is slow compared to water flow out of one of the holes), cross out 1/2pv^2 term on left

left with:

pgh= 1/2pv^2
2pgh=pv^2
2gh=v^2
sqrt(2gh)=v

the velocity exit speed will be greatest at plug 3 as it has the greatest height differential.

if need more clarification see

http://en.wikipedia.org/wiki/Torricelli's_law