It is the end of the month and you are out of gas money howe

It is the end of the month and you are out of gas money, however, there is St. Patrick\'s Day specialty clothing store you wish to visit to get ready for the big day. You discover an open, above-ground fuel tank at a nearby construction site and are tempted to use your knowledge of pressure to obtain some free gas. You slip a hose (with a diameter that is relatively small relative to dimensions of the tank) over the side of the tank in in through its top. which is 6 feet tall, until it hits the bottom of the tank. You can see that the tank is exactly half full with fuel ( is about 720 kg m ). You suck on the hose (displacing all air in hose) until gas starts to come out, but then cap it with your thumb while it sits on the ground to contemplate the ethics of your actions. Calculate: the pressure at the open end of the hose inside the tank the pressure at the highest point of the hose (don \'t consider the diameter of the hose in this calculation-the pressure here is not P ). Use your answers in (a) and (b) to determine whether or not you could effectively use your device as a siphon.

Solution

(a)

The pressure at the bottom of tank Po= P_atm + gH/2 = 101325 + 720x9.8x(6x0.305/2)= 107781 Pa

(b)

The gas which is in hose, is not flowing, and the other end is closed from thumb. Now we can use Bernoulli\'s principle, to determine Pressure at the highest point.

P_H + gH = P_o (Gas velocity is zero)

P_H + gH = P_atm + gH/2

P_H = P_atm - gH/2 = 101325 - 720x9.8x(6x0.305/2) = 94869 Pa

(c)

Now to siphon it, the thumb will have to be removed, so now the open end of the hose which is in air, will have atmospheric pressure P_atm, while the top part will have P_atm - gH/2. So the gas will not be flow in this case.