We can solve the problem using the formula shown below:
KE = 1/2 *m*v² where "m" is for the mass and "v" for the velocity
We are given with the following values:
m =?
KE = 500 J
V = 5 m/s
Mass = (KE*2)/V²
Mass = (500*2)/5²
Mass = 40 meters
The answer is 40 meters.