Project ForgeFluid Mechanics
Mechanical Operations
GATE 2015
Hard
A 1mm spherical particle falls at 1.7mm/s (downward) through a liquid (viscosity 0.04 Pa·s) flowing upward at 1mm/s (Stokes regime). The drag force per unit projected area (Pa), rounded to 2 decimal places, is
1.3 Pa(± 0.06 accepted)
Explanation
Relative velocity=1.7−(−1)=2.7mm/s. Drag/area=3πμDv/(πD²/4)=12μv/D=12×0.04×2.7×10⁻³/10⁻³=1.296 Pa.
Source: GATE CH 2015 (2015)
This question is part of a 15-day revision cycle — sign in and Project Forge will bring it back the day before you'd forget it.