# Air Pressure + Water formula

1. May 31, 2006

is there a formula which i can use to determine the the velocity of an object propelled by a gas under compression and a fluid?
thanks

2. May 31, 2006

### Andrew Mason

Can you clarify? What exactly is the problem you are trying to solve?

AM

3. Jun 1, 2006

Im given a conatainer at a set volume, with an amount of water which is given to me, both in volume and mass. I need to work out the amount of thrust which this vessel could expel, exculding the aerodynamics of the vessel.
thanks

4. Jun 1, 2006

### Andrew Mason

The thrust is given by dp/dt = vdm/dt where dm/dt is the time rate of change of mass of the system.

?? Why not just give us the problem? Is there air in the container? Are you given the pressure?

AM

5. Jun 2, 2006

okay the problem is as follows:
In a container with the volume of 1.5L, 500mL of water is introduced, as well as 100psi of air pressure. Calculate the amount of thrust this vessel will be able to provide if the air and water is allowed to escape through a 5mm opening.
if nobody is able this question, don't stress, and sorry for an inconveniences which may have been a result of my bad post.

6. Jun 2, 2006

### Andrew Mason

Assume that the water covers the hole. What is the speed at which water will be ejected through the hole? (Hint: look up Bernouilli's equation). Then determine the rate at which mass (water) leaves the container. Then just use F = dp/dt = vdm/dt to determine the thrust.

AM

7. Jun 3, 2006