5.2 Determine which of the following flow fields represent a possible incompressible flow.

(a) Vr =U cos θ; Vθ = −U sin θ

(b) Vr = −q 2πr; Vθ =K 2πr

(c) Vr =U cos θ 1− a r 2 ; Vθ = −U sin θ 1+ a r 2