Hailstones are modeled as spheres in this Fluid Mechanics drag example problem that finds the drag coefficient of a sphere and plugging into the drag equation.
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For round objects, terminal velocity is primarily dependent on Form Drag, not Friction Drag, and occurs when weight is equal to drag force (as seen on the Terminal Velocity Free Body Diagram).
Since we need Reynolds Number to find the Drag Coefficient, and we need the Drag Coefficient to Find Velocity, and we need Velocity to find Reynolds Number - we get kinda stuck - so this problem may be easiest to solve iteratively. We assume a value for drag coefficient, and solve for the velocity using drag equation then solve for Reynolds Number, and see if our guess was correct on the Drag Coefficient Figure.
TIMECODES
0:00 Terminal Velocity Free Body Diagram
1:09 Drag Force Equation
2:40 Find Density using Ideal Gas Law
5:25 Drag Coefficient Figure
8:11 Find Drag Coefficient of a Sphere
