I have a simple (?) calculation like question that I can't solve myself due to not enough knowledge. Nearly like homework question, but hopefully not. Can I ask this kind of questions here?

For the sake of a short story that I am writing currently, I need to calculate an approximate (not exact) depth to which a bullet will drill when a marksman fires it and misses totally. Bullet hits a soft soil in a city lawn.

Marks man uses 9x19 Parabellum which has approx. 396 m/s when leaving a barrel. He shots from a third floor in a direct, straight line way down toward lawn. Assuming 12 metres height plus 12 metres distance and using Pythagorean theorem, I can calculate bullet distance before it reaches ground to approx. 17 metres. And using a simple velocity formula I can assume that bullet needs approx. 0.04 second to reach the ground.

But I completely fail when it comes to calculating air and soil resistance. Assuming that this is a correct approach into calculating distance / drill-in depth of a bullet in a soil until it comes to a complete stop.

Is this a kind of question that can be asked here? Or would it be treated off-topic?


Calculation questions tend not to be well received on this site, so I think your question would be off-topic as written. In general, we are trying to help people who are interested in learning the underlying concepts in order to further their (or, sometimes, others') knowledge of physics. Doing calculations doesn't really fit in with that mission.

That being said, it's possible there might be a way to rephrase the question so that it would be on topic. If you could make some progress on the calculation yourself, and there's one small aspect of it you don't know how to deal with, you could ask about that one small aspect and it would be more likely, though not guaranteed, to be on topic. Basically, this would be the case if you're trying to teach yourself how to do the calculation, and getting the actual answer will be just a nice bonus.

  • $\begingroup$ Thank you for your enlightening and detailed answer. Does the fact that I have already made some calculations -- calculated velocity of a bullet in my example and the time, it needs to reach the ground and I only have problems calculating resistance of the ground and I to calculate how long it will take the bullet will slow down to zero and stop -- mandates as "some progress on the calculation"? Or must I go further before asking? Or ask in the chat, as suggested above. $\endgroup$ – trejder May 10 '20 at 14:09
  • 1
    $\begingroup$ The calculation you did does show that you're willing to put a bit of work into it, which doesn't count for nothing, but it doesn't really qualify on progress on the air and soil resistance calculation. So I would say you would need to put more into it to make the question on topic for the main site. The chat room may be a better fit. $\endgroup$ – David Z May 10 '20 at 18:04

I think it depends on how much calculations are involved. In my opinion, asking people to do a lot of work for the sake of an upvote is unfair. Of course, no one is obliged to do any calculations for you... but people often get passionately engaged in a discussion and may end up actually doing the calculations requested and thus losing a lot of time on an ungrateful task.


You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .