A student cycles from her home to the town library located 4.0 km due west of her home, spends some time studying, and then returns home along the same straight road before evening.
(i) Explain, with reasons, why her average velocity for the entire trip is zero.
(ii) Explain why her average speed for the same trip is not zero, and identify the physical quantity responsible for this difference.
(iii) Would the magnitude of her average velocity ever exceed the numerical value of her average speed in any journey? Justify your answer.