The same subway train later slows from 30.0 km/h (8.333 m/s) to a complete stop in 8.00 s. What is its average acceleration?

1. Average acceleration = (final velocity − initial velocity) / elapsed time. 2. Here the final velocity is 0 and the initial velocity is 8.333 m/s, so the change in velocity is 0 − 8.333 = −8.333 m/s. 3. Divide by the elapsed time: a = −8.333 m/s / 8.00 s ≈ −1.04 m/s². 4. The negative sign correctly shows the acceleration points opposite to the train's direction of travel, consistent with it slowing down (a deceleration). 5. The +1.04 m/s² option gets the magnitude right but the wrong sign; the ±0.417 m/s² options mistakenly reuse the earlier problem's 20.0 s time instead of this problem's 8.00 s. _Source: OpenStax Physics Ch 3 "Acceleration", p.101 Worked Example §3.1 Acceleration_