Archive of posts on Feb 1, 2023

• Feb 1, 2023

  Defend our earth against aliens’ bullets!

  The aliens intiated their attack to the earth! They shoot bullets with mass $m$ and speed $v$ from a far-awar planet. To defend, humans built a field $U=\alpha/r$ that can repel the bullets. What regions are safe? The answer turns out to be the interior of a circular paraboloid.

  • Categories: physics
  • Tags: calculus, classical mechanics, kepler problem, from zhihu