9. Air flows steadily through a variable sized duct in a heat transfer experiment with a speed of u = 20- 2x, where x is the distance along the duct

in meters, and uis in m/s. Because of heat transfer out of the duct, the air temperature, T, within the pipe cools as it goes downstream, according to T 200 5x °C. As they flow past the section at x= 3 meters, (a) determine the acceleration; (b) Determine th rate of change of temperature of air particles. (hint: Watch the solved video file named "Chapter 4-Temperature and Velocity.mp4")