An olympic athlete of mass 80kg competes in a 100m race. what is the best estimate of his mean kinetic energy during the race?

For this question, you need to know that the average velocity of a 100m Olympic athlete is 10 m/s before you start solving the equation. The equation is K (energy in Jules) = 1/2 mv^2 (where m is the mass in kg and v the speed in meters per second). 
The correct answer is 4000J. To see how I got it, take a look at the attachment.