Q: The force F on a sphere of radius r moving in a medium with velocity v is given by F = 6π η r v . The dimensions of η are

(a) [ML^{–3}]

(b) [MLT^{–2}]

(c) [MT^{–1}]

(d) [ML^{–1}T^{–1}]

Ans: (d)

Sol: $ \displaystyle \eta = \frac{F}{6\pi r v} $

$ \displaystyle \eta = \frac{MLT^{-2}}{ L .LT^{-1}} $

$ \displaystyle \eta = [M L^{-1}T^{-1}] $