There is an electric field at a certain point P, where initially there is no charge. A point-like object is placed at point P, and a force on the object is observed. Next the object is removed and another point-like object is placed at the same point. There is a force on this object that is different than the one observed for the first object. The following can be concluded:

Question

There is an electric field at a certain point P, where initially there is no charge. A point-like object is placed at point P, and a force on the object is observed. Next the object is removed and another point-like object is placed at the same point. There is a force on this object that is different than the one observed for the first object. The following can be concluded: 
A)The two forces must be in the same direction.
B) One of the objects has a positive charge, the other one has a negative charge
C) The two objects have the same charge but different mass.
D) The two objects must have different charges.
E) This is umpossible; the force should be the same for both objects because the electric field at the point hasn't changed

Ron · Answer

D) The two objects must have different charges.