Kinetic energy depends on the mass of object. The more is the mass the higher is the kinetic energy. With the same velocity a light tennis ball and a heavy cricket ball are thrown at you. The hit will be more by the cricket ball than that of tennis ball.
Kinetic energy also depends on the velocity of objects. The more is the velocity the higher will be the kinetic energy. The damage will be less if a truck hits a wall with less velocity but the damage will be more in case of higher velocity.
Mathematical Example: The kinetic energy of a runner of mass 70 kg is 1715 J. What is his velocity?
Mass. m = 70 kg
Kinetic energy, Ek = 1715 J
Velocity v =?
We know, Ek = ½ mv2
or, v2 = 2Ek/m
or, v = √ [2Ek/m]
= √ [ (2 * 1715 J)/70 kg] = 7 ms-1
Ans: 7 ms-1