Answer:
5 Days to Seconds = 432000
Explanation:
To develop this problem it is necessary to apply the concepts related to Gravitational Potential Energy.
Gravitational potential energy can be defined as

As M=m, then

Where,
m = Mass
G =Gravitational Universal Constant
R = Distance /Radius
PART A) As half its initial value is u'=2u, then



Therefore replacing we have that,

Re-arrange to find v,



Therefore the velocity when the separation has decreased to one-half its initial value is 816m/s
PART B) With a final separation distance of 2r, we have that

Therefore




Therefore the velocity when they are about to collide is 
Answer:
221754385964.9123
Explanation:
Convert miles to nanometer
1 mile = 1.6 km
1 km = 1×10³×10³×10³×10³ nm
1 mile = 1.6×10¹² nm
So,
158 miles = 158×1.6×10¹² = 252.8×10¹² nm
Length of each molecule = 1140 nm
Number of molecules = Total length / Length of each molecule

There are 221754385964.9123 number of molecules in a stretch of 158 miles