Kai was 200 meters north of the library when he remembered he had to return some books to the library. It took him 200 seconds to do the round trip. Which best describes Kai's roundtrip?

His speed was 2 m/s, and his velocity was 0

Explanation:

In physics, speed of an object is defined as the change in position with the change in its time. While velocity may be defined as the change in the position of the body with respect to the time taken.

Speed in a scalar quantity which means it has only magnitude while velocity has both magnitude and direction.

To determine change in velocity both direction as well as magnitude has to be changed.

In the context, Kai was 200 m of the library in the north direction. Now for the round trip to the library and back to his position, Kai took 200 seconds time to cover the distance.

So for the round trip, the speed of Kai would be 2 m/s abut the velocity of Kai is 0 as the displacement of Kai is 0.

why do the isotopes of a particular element behave differently in nuclear reactions but the same in chemical reactions? chemical reactions involve changes to electrons in an atom; isotopes do not differ in electrons, and so they react the same way during chemical changes.