Rapids

Find the speed of water flowing in the rapids?

A river narrows at a rapids from a width of 12 m to a width of 4.0 m. The depth of the river before the rapids is 2.7 m; the depth in the rapids is 0.85 m. Find the speed of water flowing in the rapids, given that its speed before the rapids is 2.2 m/s. Assume the river has a rectangular cross section.

Public Comments

1. m= mass flow rate p = density A= area v= velocity state 1: water entering control volume state 2: water leaving control volume draw a diagram and set up a control volume since no mass is lost in this process the mass entering must equal the mass exiting the system so m1 = m2 p1A1V1=p2A2v2 assuming density is the same a1v1=a2v2 v2 = a1v1/a2 a1 = 12* 2.7=32.4 m^2 a2 = 4*0.85=3.4 m^2 v1 =2.2 m/s v2 =20.96 m/s