A sailboard is gliding across a lake at a speed of \(20 \mathrm{mph}(9 \mathrm{~m} / \mathrm{s})\). The sailboard is \(3 \mathrm{~m}\) long, \(0.75 \mathrm{~m}\) wide and represents a smooth, flat surface. Using the physical properties for water listed below:

\(ho=997.5 \mathrm{~kg} / \mathrm{m}^{3} \quad \mu=9.8 \times 10^{-4} \mathrm{Ns} / \mathrm{m}^{2} \quad C_{p}=4179 \mathrm{~J} / \mathrm{kg} \mathrm{K}\)

\(k=0.604 \mathrm{~W} / \mathrm{m} \mathrm{K} \quad \operatorname{Pr}=5.85\)

a. What is the average friction factor for the sailboard?

b. What is the average shear stress on the sailboard?

c. How much power must the wind provide to propel the sailboard?