Two positively-charged objects are located 0.1 m apart.

Question

How does the value of their mutual electric force change if the distance between them is doubled?
(A) quadruples (B) doubles (C) same (D) halved (E) one-fourth

How does the value of their mutual electric force change if the distance between them is halved?
(A) quadruples (B) doubles (C) same (D) halved (E) one-fourth

How does the value of their mutual electric force change if the charge on one object is doubled?
(A) quadruples (B) doubles (C) same (D) halved (E) one-fourth

How does the value of their mutual electric force change if the charge on both objects is doubled?
(A) quadruples (B) doubles (C) same (D) halved (E) one-fourth

How does the direction of their mutual electric force change if the sign (positive or negative) of one of the charges changes?
(A) same direction as originally (B) opposite direction

How does their mutual electric force change if the sign of both charges changes?
(A) same direction as originally (B) opposite direction
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Answer 1

Now wait a minute. What do you think?

repulsive force = k Q1 Q2 / R^2

hint, if signs the same, repulsion. Like charges repel.
2^2 = 4 so (1/2)^2 = 1/4