In outer space, two small balls of equal unknown masses and charges +q and −q are held at rest a distance d o apart. Then the balls are simultaneously launched with equal speeds v o in the opposite directions that are perpendicular to the line connecting the balls. During the subsequent motion of the balls, their minimum speed is v. Find the masses of the balls.

We received a large number of solutions, not all of them correct, for our November Challenge, 2t or Not 2t? Many of the solutions came from the first-time contributors, including several high school students. We are pleased to recognize the following authors of correct solutions:

Sharmila Balamurugan, undergraduate student (Women's Christian College, Chennai, India)

Salvatore Basile (Università degli Studi di Palermo, Palermo, Italy)

Tyriek Bayne, student (John Tyler Community College, Midlothian, VA)

Wojciech Bizoń (Jagiellonian University, Cracow, Poland)

Philip Blanco...

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