Water leaves a tap where the cross-sectional area is 2.0 cm² with a speed of 3 m/s. Taking g = 10 m/s², what is the cross-sectional area of the falling water column at a point 80 cm below the tap?

0.6 cm²
1.2 cm²
1.5 cm²
2.0 cm²

Correct answer: 1.2 cm²

Solution

The stream accelerates under gravity so it speeds up and thins. Find the new speed from free-fall kinematics, then conserve volume flow rate.

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