Water flowing along an open channel drives an undershot waterwheel of radius 2 m (figure). The water approaches the wheel with a speed of 5.0 m/s and leaves with a speed of 2.5 m/s; the amount of water passing by is 200 kg per second. At what rate does the water deliver angular momentum to the wheel (in kJ) ?

Question

G1 Physics · Accepted Answer

Angular momentum flow rate about the wheel axis is τ̇ equivalent to ṁR(incoming speed-outgoing speed). With ṁ=200 kg/s, R=2 m, incoming speed=5.0 m/s and outgoing speed=2.5 m/s, rate =200×2×(5-2.5)=1000 N·m =1 kN·m, so the numerical answer is 1.