Uranium-235 decays to thorium-231 with a half-life of 700 million years. When a rock was formed, it contained 6400 million uranium-235 nuclei and no thorium-231 nuclei. Show that after 2100 million years there are seven times more thorium nuclei than uranium nuclei in the rock.

proof in explanation

Explanation:

First, we will calculate the number of half-lives:

where,

n = no. of half-lives = ?

t = total time passed = 2100 million years

= half-life = 700 million years

Therefore,

Now, we will calculate the number of uranium nuclei left ():

and the rest of the uranium nuclei will become thorium nuclei ()

dividing both:

Hence, it is proven that after 2100 million years there are seven times more thorium nuclei than uranium nuclei in the rock.

molecules are free to separate from each other and will take on the shape of the container. molecules move completely at random and high speeds. they vibrate in a fixed position and do not move around much. molecules expand to the edge of their container.

490 n

f=125n a=2.5m/s2