Answer:
4.30 x 10⁵ N/C
Explanation:
Two positive +3.0-μC point charges at opposite corners of the square creates equal and opposite electric field at the center. hence the electric field by these two positive charges at opposite corners becomes zero.
= length of the square of side = 0.50 m
= distance of the center from each corner = 
Magnitude of net electric field at the center is given as

Answer:
B
Explanation:
Given that an elevator moving down passes its neighbor, an elevator moving up. Their speed relative to one another is 8 m/s. What is the velocity of each elevator relative to someone standing on the first floor? Assume that the elevators are traveling at the same speed, and that the upward direction is
positive.
Solution
Given that upward direction is positive, then, the downward direction will be negative.
To get a relative velocity of 8m/s
4 - ( - 4 ) = 8
Therefore, the correct answer will be
One elevator is moving at 4 m/s; the other elevator is moving at -4 m/s
Which is option B
Because the negative multiply by negative sign will give positive sign.
Given
4 + 4 = 8.