Chapter 9, Problem 118P

While walking across campus one windy day, an engineering student speculates about using an umbrella as a “sail” to propel a bicycle along the sidewalk. Develop an algebraic expression for the speed a bike could reach on level ground with the umbrella “propulsion system.” The frontal area of bike and rider is estimated as 0.3 m², and the drag coefficient is about 1.2. Assume the rolling resistance is 0.75 percent of the bike and rider weight; the combined mass is 75 kg. Evaluate the bike speed that could be achieved with an umbrella 1.22 m in diameter in a wind that blows at 24 km/hr. Discuss the practicality of this propulsion system.