The relativistic increase in mass of the metal ball due to velocity (70 times) x 5 kg means the ball will have an effective mass of 350 kilograms , put that into

E= (70 times) mc^2 and convert the energy released into tons of TNT results in:

E = 31,050,000,000,000,000,000 Joules which is equivalent to Approx 7,500,000,000 Ton’s of TNT (7.5 Billion Ton’s).

All this energy will be applied to an area equal to a circle with a diameter of the metal ball 4 inches (106mm), assuming its made from iron .That will give it a volume of 635cc or 38.5 cu.in and a Circle area 13.6 sq inches (88 sq cm^2 ).

Therefore 7.5 Billion Ton’s of TNT energy equivalent will be applied to an area of 13.6 sq inches of the metal ball as it enters the earths atmosphere . What will happen ? First off the ball will not even “see” the atmosphere , it will literally cut a hole through it.

Whether it hits the land or sea makes no difference and I think it will deposit all its energy (stop!) within 2-300 km below the surface. I do not believe it will have the capability to pass right through the earth but most of the energy will be deposited sub-surface.

Because of the small size of the ball but huge energy released the fireball will have a very high temperature at onset (10’s million of degrees) also a huge crater will be produced that maybe 10-15km deep and 40 km in diameter.

There is also a chance that the incredible energy deposited in such a small area at the onset (the atmosphere ) may have capability of Atomic fusion , fission reactions being generated ? even Neutrons , gamma rays and x -Rays at high flux ?

See below Fig 2 . Some estimations of 7.5 Billons of TNT equivalent energy release centered on New York city !

Green circle : Fireball radius: 17.07 km / 10.61 mi : 20 psi overpressure; heavily built concrete buildings are severely damaged or demolished; fatalities approach 100%.

Blue circle : Air blast radius: 137.4 km : 4.6 psi overpressure; most buildings collapse; injuries universal, fatalities widespread.

Gold circle : Thermal radiation radius: 453.21 km / 281.61 mi : Third-degree burns to all exposed skin; starts fires in flammable materials, contributes to firestorm if large enough.