Please help me solve this example in the book "Theoretical mechanics"?

This question seems extremely vague considering the generalization of the term "particle" . Sub-atomic particles are racing and bouncing off each other in wonderful harmony. A particle of organic or gins could be fluttering along lackadaisically ay the same time with other particles traveling through it, but the human eye sees only the beauty of airborne spec. Assuming this "particle" was visible i would refer to Sir Issac Newton's laws of gravity to answer the remainder of the question.