9.20 A 0.3 m diameter circular disk is placed normal to a flow stream that has a speed of 5 m/s. Calculate the force and power if the fluid is

(a) air and

(b) water. If the disk is replaced with a hemisphere with the open end facing downstream, determine the power for the two fluids. Explain why there is a difference for the two geometries even though the frontal area is the same.