Explanation:
It varies with altitude, but at sea level, it's 9.8 m/s².
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 
Silver sable is in spiderman lol
Answer:
10
Explanation:
Lets say that a,b,c,d,e are the five allowed energy states in order of decreasing energy. Then the number of possible different spectral lines comes from the electron dropping from a high state to a lower state. So, they will do so in following ways:
a - b
a - c
a - d
a- e
b - c
b - d
b- e
c - d
c- e
d- e
Ans- Ten different possible energy jumps giving six different colors or lines in the spectrum.
Average speed = (total distance covered) / (time to cover the distance)
Total distance covered = (9.5m + 3.5m + 15m) = 28 meters
Time to cover the distance = 43 seconds
Average speed = (28 meters) / (43 seconds)
Average speed = 0.65 meters/second