Answer to Question #134710 in Physics for thati

Question

Charges Q and 5Q are located on the x-axis as shown in the
Figure. When a third charge is placed at the origin, it is found
that the force on it is zero.
(a) What is the sign of the third charge? Explain your
answer. (2)
(b) Find the value of α.

Answer 1

(a)

The sign of the charge can be both positive and negative, because the forces acting on it by the other two charges are opposite.

(b)

$kQq/L^2=k5Qq/(\alpha L)^2\to \alpha=\sqrt5$