Two identical cubes have mass m and side r each. The cubes rest very close to each other on a large horizontal table as shown. A uniform sphere of mass m and radius r is gently placed on top of the cubes as shown. Once the sphere is released, it begins to push the cubes apart and slide downward. The acceleration due to gravity is g. Find the speed v of the sphere at the moment it hits the table. Express your answer in terms of the given quantities and a numeric coefficient with at least three significant figures. Neglect friction between all surfaces.

We received a large number of solutions (not all of them correct) to our September Challenge, C'est la v. It was gratifying to see quite a few new participants, including many high school students from all over the world. (It was slightly less...

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