A father racing his son has one-third the kinetic energy of the son, who has two-fifths the mass of the father. The father speeds up by 2.5 m/s and then has the same kinetic energy as the son.

Answer 1

Sam,

By reposting 4 times (plus the original) in a matter of minutes, you are not helping the system.

Either someone has to spend the time deleting your duplicate posts instead of making a response (which is the present case), or all physics tutors have to spend time reading the same post over 5 times, thus reducing the time spent on responding.