Two small metal spheres are connected by a light flexible metal wire of length l. The spheres have equal radii r (r<<l) but different masses: m and 2m. Initially, the spheres are held at rest on a large insulating frictionless table at a distance l/2 from each other in a uniform electrostatic field of magnitude E, directed along the straight line connecting the spheres.

The spheres are released simultaneously. Find the maximum speed v attained by the sphere of mass m.

We received quite a few solutions to our December Challenge, Defying gravity in a cavity, but not all of them were correct.

We are pleased to recognize the following contributors:

  • Dave Allen, a mystery man

  • Wayne R. Anderson (Sacramento City College, Sacramento, California, emeritus)

  • R.R. Bukrey (retired, Loyola University, Evanston, IL)

  • Riccardo Burlon (Università degli Studi di Palermo, Palermo,...

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