2020 elastic balls of equal size but different masses m1, m2, ….m2020 are placed d = 1.00 m apart inside a very long straight horizontal pipe. The balls are numbered consecutively, from 1 to 2020. The ball numbered “1” is the heaviest. For all other balls, m(n+1) = kmn where k = 0.99.

At t = 0, the “first” ball is given the velocity of v0 = 0.100 m/s toward the “second” one. Neglecting friction and assuming that the collisions between the balls are elastic and instantaneous, find the moment T when the 2020th ball begins to move, and its initial velocity v.

We received quite a few well-written and detailed solutions to our September Challenge, A fall with a bang. A great start of the fall season indeed.

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