A rider on a mountain bike is traveling to the left in the figure. Each wheel has an angular velocity of + 21.7 rad/s, where, as usual, the plus sign indicates that the wheel is rotating in the counterclockwise direction.
(a) To pass another cyclist, the rider pumps harder, and the angular velocity of the wheels increases from + 21.7 to + 28.5 rad/s in a time of 3.50 s.
(b) After passing the cyclist, the rider begins to coast, and the angular velocity of the wheels decreases from + 28.5 to + 15.3 rad/s in a time of 10.7 s. Concepts: (i) Is the angular acceleration positive or negative when the rider is passing the cyclist and the angular speed of the wheels is increasing? (ii) Is the angular acceleration positive or negative when the rider is coasting and the angular speed of the wheels is decreasing? Calculations: In both instances, (a) and (b), determine the magnitude and direction of the angular acceleration (assumed constant) of the wheels.