Why is large-scale nuclear fission a rare phenomenon on Earth?

Large-scale nuclear is fission a rare phenomenon on Earth because

atoms that undergo fission aren't concentrated enough to sustain a chain reaction.

Atoms that undergo fission aren't concentrated enough to sustain a chain reaction. For example, the decay chain of U-238 is called the uranium series. ... Uranium is find in ores on Earth with very law mass percentage in it, so fission is not possible

a: 45.9 meters

b: 4.29 seconds

step-by-step explanation:

a: h(t)=1/2(-9.8)(3)^2+0(3)+90

h(t)=-4.9(3)^2+90

h(t)=-44.1+90

h(t)=45.9 meters

b: 0=1/2(-9.8)(t^2)+0t+90

0=-4.9t^2+90

-90=-4.9t^2

18.37=t^2

t=4.29 seconds

in the second question, the numbers aren't exact, but they're a close approximation.

idk what is it? is this a question that you know the answer or u dont