A train traveled 100 kilometers north in 2 hours. After exchanging some railroad cars, it traveled 100 kilometers south in 2 hours along the same track. Why has the train's velocity changed

Due to change in direction

Explanation:

Given

Initially train has traveled a 100 km in North and after exchanging some railroad cars, it traveled 100 in south.

The velocity of the train changes as it direction of motion changes. Velocity is the vector quantity which require direction and magnitude for its reperesentation.

multiple allele inheritance is traits controlled by more than 2 alleles (ex: pigeons having 3 alleles of one gene govern their feather color).