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Real-Life Math -- Solution

You need to find out if you can use an aluminum rod measuring 20 millimeters in diameter in your design.

Stress = load / area

Area of the rod:

Area = 3.14 (20 mm / 2)2
Area = 3.14 x 102
Area = 314 mm2

Now you need to convert your area to squared meters.

1 mm2 = 10-6m2
Area of the rod = 314 mm2 x 10-6m2

Stress = load / area

Stress = 50 x 103 newtons / 314 x 10-6m2
Stress = 50,000 newtons / 0.000314 m2
Stress = 159 x 106Pa

The allowable stress on aluminum is 100 x 106Pa.

From your calculations, you've determined that an aluminum rod 20 millimeters in diameter will not be able to withstand the load placed upon it. You'll probably have to choose another lightweight, strong material, such as titanium.

"I was always good with math," says Kostyantyn Khomutov, an aerospace engineer. "I always had an interest in numbers, with calculations. And I always was fascinated by how the world works and physics, chemistry and biology."


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