The formula of the kinetic energy is KE = 0.5*m*v^2.
Given m = 80 kg and KE = 4000 J,
4000 = 0.5*80*v^2
v^2 = 100
v = 10 m/s
The answer is : <span>Planetesimals, protoplanets, planets. This is the order of the celestial body from earliest to latest. </span><span>A </span>protoplanet<span> is a massive object that will eventually become a planet. </span><span>They are at first formed by the accumulation of </span>planetesimals<span> into </span>protoplanets<span>, then into planets.</span>