Question

The discharge and velocity of water in a rectangular channel are 75m^3/s and 5m/ s respectively. The hydraulic depth being 3m calculate the hydraulic radius.

(a) 1.36m

(b) 1.87m

(c) 1.98m

(d) 2.0m

This question was addressed to me in examination.

This key question is from Geometrical Properties of Rectangular Section topic in division Flow in Open Channels of Fluid Mechanics

Answer 1

Correct option is (a) 1.36m

Best explanation: Discharge (Q) = (A) (V)

75 = (A) (5)

A = 15m^2

A = (B) (y)

B = 15/ 3 = 5m

R = A/ P = 15/ (5 + 2(3))

R = 1.36m.