**P. 4072.** Two pointlike particles of charge *Q* are fixed at two of the vertices of an equilateral triangle of sides . At the third vertex a third particle of mass *m* and of charge *q *is released.

What is the initial acceleration of this particle, and with what speed does it pass one of the the points which is at a distance of 2 from both the fixed charges? How does the result change if the effect of the gravitational force is considered as well while the particle moves along a vertical line?

*Data:* =10 cm, *m*=10^{-3} g, *Q*=10^{-8} C, *q*=10^{-9} C.

(5 points)