Fluid Mechanics
In case of hydraulically smooth pipe, the resistance to flow depends only on the Reynolds number, whereas for a hydraulically rough pipe, the resistance to flow is governed by the relative roughness. Two pipes are said to have the same hydraulic roughness, when they have equal values of

Friction co-efficient for flows at equal Reynold number
Absolute roughness
All of these
Relative roughness

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Fluid Mechanics
A stream line is

Drawn normal to the velocity vector at every point
A line connecting the mid points of flow cross-section
Always the path of particle
Fixed in space in steady flow

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