Diameter of first pipe, d1=2cm ∴ Radius, r1=1cm=10−2cm Diameter of second pipe d2=4cm ∴r2=2cm=2×10−2m If v1 and v2 are the velocities of water in first and second pipe respectively, then according to principle of continuity, A1v1=A2v2⇒πr12v1=πr22v2