HardPhysicsHigh School (11–12)Mechanics › Fluid Flow, Bernoulli's Principle and ViscosityNumericalBoard Exam AP

A small plane has wings of total area 25 m²…

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A small plane has wings of total area $25\ \text{m}^2$ . In level flight, air moves at $75\ \text{m/s}$ over the top of the wings and $65\ \text{m/s}$ under them. Find the pressure difference, the lift, and the largest mass the plane can have in level flight. (Air $1.29\ \text{kg/m}^3$ , $g = 9.8\ \text{m/s}^2$ .)

Need a reminder? The key ideaShow

Torricelli's law: water leaves a hole $h$ below the surface of an open tank at $v = \sqrt{2gh}$ . A Venturi meter finds the speed of flow from the pressure drop in its throat. Fast air has low pressure, which lifts wings and roofs.

The worked solution

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Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.

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