Hot, soft rock rise from the bottom of the mantle towards the top, cools, and sinks back through the mantle.
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:
The true course:
north of east
The ground speed of the plane: 96.68 m/s
Explanation:
Given:
= velocity of wind = 
= velocity of plane in still air = 
Assume:
= resultant velocity of the plane
= direction of the plane with the east
Since the resultant is the vector addition of all the vectors. So, the resultant velocity of the plane will be the vector sum of the wind velocity and the plane velocity in still air.

Let us find the direction of this resultant velocity with respect to east direction:

This means the the true course of the plane is in the direction of
north of east.
The ground speed will be the magnitude of the resultant velocity of the plane.

Hence, the ground speed of the plane is 96.68 km/h.
Answer:
The resistance in first case is 12 Ω, power delivered is 12 W, and potential difference is 0.01 V
Explanation:
Given:
(A)
Current
A
Voltage
V
For finding the resistance,



12Ω
(B)
For finding power delivered,


Watt
(C)
For finding the potential difference,



V
Therefore, the resistance in first case is 12 Ω, power delivered is 12 W, and potential difference is 0.01 V