Pa−Pn=24 PaLet the speed of blood in artery and narrow part be va and vn respectively.
From continuity equation : Aava=Anvn
∴ 8va=4vn
⟹vn=2va
Using Bernoulli's equation :
Pa+ρgha+12ρv2a= Pn+ρghn+12ρv2n
where hn=hn
∴ Pa−Pn=12ρ(v2n−v2a)
∴ 24=12×1.06×103(4v2a−v2a)
⟹ va=12.5×10−2 m/s