A small block of mass m is moving at a speed v along a horizontal floor toward an inclined plane of mass 4m that makes the angle θ with the horizontal. The block slides up and back down the inclined plane. How much time does the block spend on the plane? Assume that the transition from the floor to the inclined plane is smooth and that all surfaces are frictionless.

We received many solutions to our September Challenge, Know your ABC’s. We are pleased to recognize the following contributors:

Guidelines for contributors

Many thanks to all contributors and we hope to hear from many more of you in the future!

Note: as always, we would very much appreciate reader-contributed original Challenges.

Boris Korsunsky, Column Editor

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