A spherical tank for storing gas under pressure is 25 m in diameter and made of steel 15 mm thick. The yield point of the material is 240 MPa. A factor of safety of 2.5 is desired. What is the maximum permissible internal pressure?

electric field is a function of 1/r^2

yes, the force per unit charge for a point charge is inverse square law.

no. bullets are macro objects. wave nature is for light waves, extremely tiny particles. if a light particle was the size of your finger, the bullet would be the size of the universe. so basically, that huge difference in size makes the wave nature of matter insignificant.