Look at it this way:
Every time the plane flies through 400 miles of air,
the air moves it 40 miles backwards.
So it only covers 360 miles of ground in an hour.
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Divide the flow rate (0.750 m³/s) by the cross-sectional area of each pipe:
diameter = 40 mm ==> area = <em>π</em> (0.04 m)² ≈ 0.00503 m²
diameter = 120 mm ==> area = <em>π</em> (0.12 m)² ≈ 0.0452 m²
Then the speed at the end of the 40 mm pipe is
(0.750 m³/s) / (0.00503 m²) ≈ 149.208 m/s ≈ 149 m/s
(0.750 m³/s) / (0.0452 m²) ≈ 16.579 m/s ≈ 16.6 m/s
