alleryStart learning →A cyclist rides 3 km west and then turns around and rides 2 km east. Taking west as the positive direction, what is her displacement?
A1 km east
B1 km west
C5 km west
D5 km east
Answer & Solution
Correct answer: B. 1 km west
1. Take west as positive, so the first leg is +3 km and the second leg is -2 km.
2. Displacement is final position minus initial position: (+3 km) + (-2 km) = +1 km.
3. A result of +1 km in a west-positive axis means 1 km west of the start.
4. This is smaller than the 5 km she actually rode, because displacement ignores the doubling back.
_Source: OpenStax Physics (CC BY 4.0), Ch 2 "Motion in One Dimension", section 2.1 Relative Motion, Distance, and Displacement_
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