The answer is either
b A system in which Newton's Laws are valid
or
c A system in which there are no external forces.
Explanation:
not a, and not d
There are energy changes in a closed system.
A closed system obeys the conservation laws in its physical description.
A materiel that allows electricity to flow easily is called an conductor
Answer:
The <em>net gravitational force it exerts</em> is 
Explanation:
Newton's Law of Gravitation can be written as

where <em>G is the Gravitational Constant, m1 and m2 are the masses of two objects, and r is the distance between them</em>. In this case, the spheres are loacted in straight line, so instead of a vector r, we have a distance x in meters. The distances and masses are given in the problem, and the smaller sphere is between the other two spheres. This means <u>the sphere 1 is in the middle, the sphere 2 is on the left of 1, and the sphere 3 is on the right of 1</u>, so
is the force that 2 feels because of 1, and
is the force that 3 feels because of 1.
<em>If we replace the data in those previous equations</em>, we have that


Finally, adding both results, the net force the sphere 1 exerts is

Direction of |a+b| is south east and that of |a-b| is north east.
<h3>Calculation:</h3>
Given
a = 3i - 2j
b = -i - 4j
To find,
a+b =?
a-b =?
|a+b| = |(3i - 2j - i - 4j)|
= |2i - 6j|
= 
= 
= 
= 
|a-b| = |(3i - 2j) - (-i - 4j)|
= |3i -2j + i + 4j|
= |4i + 2j|
= 
= 
= 
= 
Direction of |a+b| is south east (|2i - 6j|, this shows 2 units to the right and 6 units down)
Direction of |a-b| is north east (|4i + 2j|, this shows 4 units right & 2 units up)
Learn more about vector calculation here:
brainly.com/question/27351405
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