Answer:
K'=4K
Explanation:
The electric potential energy is given by :

Where
k is spring constant
x is compression or extension in the spring
If the displacement of a horizontal mass-spring system is doubled, x'= 2x
New elastic potential energy :

So, new elastic potential energy 4 times the initial elastic potential energy.
Base on my research, within 2 hours you have a number of atoms which remain.
N= N0*2^(-t/6.020 = N= N0*2^-0.33223= 07943 N0
So, the number of atoms that are being disintegrated is N0-N=N0*(1-0.79430)=0.2057 N0
It must be equal to 15 mCi = 15*3.7*10^7= 5.55*10^8 atoms
N0= 5.55*10*8/0.2057 = 2.698*10^9 atoms
Therefore, 2.698*10^9 atoms is the number of N0
<span>♦The gas may become a liquid as it loses energy♦</span>