Question Energy of a Low Earth Orbit collision - is this calculation correct?

Nov 3, 2021
Hello, could someone kindly double check my math?
Alternatively: is there a better place to post the request?

My calculation:
50 gram mass (0.05 kg)
Low Earth Orbit (~8 km/sec)
Head on collision (relative velocity 16 km/sec)
Kinetic Energy = 1/2 * mass * velocity_squared

Kinetic energy released in bolt's impact on a spacecraft: 6.4 million joules, equivalent to 1.5 kg of TNT

Same energy as.... mass moving at bullet speed (760 m/sec), where the mass = 22.16 kg.

That's 50 lbs moving at the speed of a bullet! Could that possibly be right? Colliding head on with a bolt in Low Earth Orbit packs the same punch as being shot by a 50 lb dumbbell? Seems extreme!

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Last edited by a moderator:
Nov 3, 2021
In case there was missing context, this is the setup
(a link to which was removed by moderation):

The energy of a Low Earth Orbit collision
Imagine hitting something head-on at a clip of 8,000 m/sec in opposite directions. Physics tells us kinetic energy is proportional to the SQUARE of the velocity… Which is already starting at 16,000 m/sec (relative).

Kinetic energy is proportional to the velocity squared
To compute the energy in standard SI units we can use mass in kilograms and velocity in meters/second.

Say we’re talking about a medium sized bolt, about 50 grams (0.050 kilograms). A head on collision, with both objects moving at a relative velocity of 16,000 meters/second.

E = 1/2 (0.05) (16000) (16000) = 6,400,000 joules.

Do the math, and we find - if this 50gm bolt smashes into us at 16,000 m/sec it’s packing a 6,400,000 joule punch, which is equivalent to 1.5 kg of TNT. That’s a lot, for a small space.

A bullet the size of a dumbbell walks into a bar
An average bullet travels at 760 meters/second. So, how big would a bullet need to be to pack a 6,400,000 joule punch?

6,400,000 = 1/2 (mass) (760)(760)
mass = 22.16 kg.



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