Well, you have part of what you need to know to get the kinetic energy of Arnel. Kinetic energy is the energy produced by moving things, or things that move. The formula for kinetic energy is : KE = 1/2mv2, or kinetic energy equals one-half the mass times the square of the velocity. You have the velocity, which is 15 meters per second, but you need the mass. How much mass does Arnel have in his body? On the other hand, if you already know how much kinetic energy is being produced, to find the mass, you could square the velocity, which would be 225, then multiply both sides times 2 to get rid of the 1/2 on the right side of the equation. Divide the left side by the 450 that was produced on the right side of the equation, and that would give you Arnel's mass. The mass would probably be expressed in kilograms, since we are talking about the weight of an a human body.