Two conducting spheres have mass m and radius r each. One of them has a charge +q, and the other has a charge of (–3q). Initially, the spheres are held at rest on a large frictionless insulating horizontal plane. The distance between the centers of the spheres is L.

After the spheres are released, they collide elastically, and their charges equalize. Find the speeds of the spheres when they are far away from each other. Neglect all polarization effects.

We received many solutions for our December Challenge, Good-bye, 2020! We are pleased to recognize the following successful solvers:

Juan M. Aguirregabiria (University of the Basque Country, Bilbao, Spain)

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

Phil Cahill (The SI Organization, Inc., Rosemont, PA)

Norman Derby (Southwestern Oregon Community College, Brookings, OR)

Don Easton (Lacombe, Alberta, Canada)

José Ignacio Íñiguez de la...

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