A commuter train runs from one station to another and back again. Why is its average velocity for the whole run zero?
ABecause the elapsed time is longer than one hour
BBecause the return leg is slower than the outward leg
CBecause the total distance travelled is counted twice
DBecause the final position equals the initial position
Answer & Solution
Correct answer: D. Because the final position equals the initial position
1. Average velocity is the displacement divided by the elapsed time.
2. The train ends up at the same place it starts, so the final position equals the initial position.
3. The displacement is therefore zero, and so is the average velocity.
4. The average speed is not zero, since the total distance travelled is not zero.
_Source: OpenStax College Physics (CC BY 4.0), Ch 2 "Kinematics", section 2.3 Time, Velocity, and Speed_
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