Kinetic energy is defined as the energy is being used to do an activity, basically energy associated with the motion of objects in the universe.
The formula used to find the kinetic energy of an object is k = where as k represented as kinetic energy, m is the mass of the object and v is the velocity of the given object.
Here, to find the answer we have to re-write the equation as
Given, the mass of the object, here it is John = 80 kg, energy needs to be converted to kinetic energy, k = 1000 J.
Hence, substitute all the values, then you would velocity as 5 m/s