Answer: 
Explanation:
We can solve this with the Law of Universal Gravitation and knowing the acceleration due gravity
of an object above the surface of the planet decreases with the distance (height) of this object from the center of the planet.
Well, according to the law of universal gravitation:
(1)
Where:
is the module of the force exerted between both bodies
is the gravitational constant
is the mass of the Earth
are the mass of each communications satellite
is the distance between the center of the Earth and the satellite
is the radius of the Earth
is the height of the satellite, measured from the Earth's surface
On the other hand, we know according to <u>Newton's 2nd law of motion:</u>
(2)
Combining (1) and (2):
(3)
Isolating
:
(4)
Remembering
:
(5)
Finally:
The final velocity is 1.37 m/s east
Explanation:
We can solve this problem by using the law of conservation of momentum: in fact, in absence of external forces, the total momentum of the two trains must be conserved before and after the collision.
So we can write:
where:
is the mass of the first train
is the initial velocity of the first train (we take east as positive direction)
is the mass of the second train
is the initial velocity of the second train
is the final combined velocity of the two trains
Re-arranging the equation and substituting the values, we find:

And the positive sign indicates their final direction is east.
Learn more about momentum here:
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A -..................................is the correct option
To find the answer, plot down the factors for every number.
12: 1, 2 ,3 ,4, 6, 12
18: 1, 2, 3, 6, 9, 18
84: 1, 2, 3, 4, 6, 7, 12
If you noticed, the number that was common to the 3 numbers, were 1, 2, 3, and 6
And 6 is the bigger number
So 6 is your GCF
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