A subway train accelerates from rest to 30.0 km/h (8.33 m/s) in 20.0 s. What is its average acceleration?

1. Average acceleration = change in velocity / change in time. 2. The train starts from rest, so the change in velocity is simply the final velocity: 8.33 m/s − 0 m/s = 8.33 m/s. 3. Divide by the elapsed time: a = 8.33 m/s / 20.0 s ≈ 0.417 m/s². 4. 8.33 m/s² wrongly treats the velocity value itself as the acceleration; 20.0 m/s² wrongly treats the time value as the acceleration; 1.50 m/s² does not correspond to either given number divided correctly. 5. So the train's average acceleration is about 0.417 m/s², directed the same way as its motion since it is speeding up. _Source: OpenStax Physics Ch 3 "Acceleration", p.101 Worked Example §3.1 Acceleration_