Three runners are competing in a 120-m race. Each begins when the starting signal sounds and all three runners cross the finish line at the same time. The first runner moves at a constant speed of 6 m/s. The second runner sprints at a constant speed of 7.5 m/s, stops after 60 m to rest for 4 s, then runs the second half of the race at a constant speed of 7.5 m/s. The third runner dashes 60 m at a constant speed of 12 m/s but realizes they forgot their keys, so runs back to the starting line at a constant speed of 12 m/s, then turns around and runs straight to the finish line at a constant speed of 12 m/s. Which of the following statements about this situation is NOT true?
Assume all average velocities and average speeds are for the period from the starting signal to the moment the runners cross the finish line. You may select more than one option.
a. The average speed of the third runner is not equal to his average velocity
b. The average velocity of the third runner is zero.
c. The first runner's average velocity is equal to the second runner's average velocity
d. The second runner's average speed is less than 7.5 m/s.
e. All three runners have the same average velocity.