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Physics/Hoping you're the right person for a force based question.


Dear Mr. Johnson
  Math has never been my strong point, but recently I've grown curious. It relates to a game I have. In this game it claims that a 44lbs, piece of metal

(it didn't say what kind of metal, but based on the game it's probably Tungsten)

Anyway it claims a piece of metal weighing 44lbs, traveling at 8,720,020 Miles per Hour, would hit with the force of a 20 kiloton nuke.

If it is within your expertise, may I please ask if their assessment is correct? Or is it way too high, or way too low?

Thank you for taking the time to read my question.

Hello Alex,

I do not think force is the parameter that is the best measurement for this comparison. Consider: if you are going down the road at 60 mph and hit a fly, the force applied to the fly is a lot smaller than if you hit a large bird. If you set up situation, and wanted to compare the damage the 44 pound piece of metal and the 20 kt nuke would do to a specific object, that could be compared. But I think you want to compare the energy available to the  piece of metal and to the 20 kt nuke.

The energy yield of a detonation of a 20 kt nuke is about 84 TJ (84*10^12 Joules).
A piece of metal weighing 44lbs, traveling at 8,720,020 Miles per Hour possesses energy due to its speed. That is called kinetic energy and the formula is
KE = (1/2)*m*v^2
To find the KE of this piece of metal and compare it to the number of Joules released by the nuke detonation, we need to convert the units to SI units.
The mass of 44 lbs is 20 kg.
8,720,020 Miles per Hour converts to 3,898,198 m/s. Let's call it 3.9*10^6 m/s. So the kinetic energy is
KE = (1/2)*20 kg*(3.9*10^6)^2 = 152*10^12 Joules

So your speeding chunk of metal has about 1.8 times as much energy as the nuke would release. If the metal hit the Earth like a big meteor, all that energy would be dissipated making a big crater (and a big fire and throwing a lot of dirt into the air).

I hope this analysis is applicable to the situation in your game.


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Steve Johnson


I would be delighted to help with questions up through the first year of college Physics. Particularly Electricity, Electronics and Newtonian Mechanics (motion, acceleration etc.). I decline questions on relativity and Atomic Physics. I also could discuss the Space Shuttle and space flight in general.


I have a BS in Physics and an MS in Electrical Engineering. I am retired now. My professional career was in Electrical Engineering with considerable time spent working with accelerometers, gyroscopes and flight dynamics (Physics related topics) while working on the Space Shuttle. I gave formal classroom lessons to technical co-workers periodically over a several year period.

BS Physics, North Dakota State University
MS Electrical Engineering, North Dakota State University

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