Answer:

Explanation:
h = Planck's constant = 
m = Mass of electron = 
k = Coulomb constant = 
e = Charge of electron = 
n = 1 (ground state)
Angular momentum is given by

From Bohr's atomic model we have


The centripetal force will balance the electrostatic force

The diameter is 
If you could please give me a already given speed I could estimate it. since there is no speed shown you wouldn't be able to estimate the speed of the moving train.
Answer:
a)
, b) 
Explanation:
a) The potential energy is:



b) Maximum final speed:

The final speed is:


Structural constraint is the answer :)