AP Physics B : Fluid and Gas Mechanics
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Example Questions
Example Question #1 :Understanding Bernoulli's Equation
An incompressible fluid flows without viscosity at
The mass density of the fluid is
If the fluid is incompressible and flows without viscosity in a confined space, then an equal volume must move past any point in that space in the same time interval, even if the geometry of the confines changes. An equal volume must pass Points
Since the diameter of the section on the right is smaller, the fluid must move faster in that region for an equal volume to pass by point
In this problem, the flow speed in the larger section of pipe is
Hence, the flow speed in the smaller section of pipe is
Now use Bernoulli’s principle, which expresses conservation of energy in fluid flow as:
Pressure + kinetic energy of flow + fluid potential energy = constant
Fluid potential energy depends on height (like gravitational potential energy), and so does not change from one part of the pipe to the other. So, for this case, Bernoulli's principle becomes:
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