A small disc of mass m is held at rest at the edge of a hemispherical cavity made in a solid block of mass 3m. The block is placed on a horizontal surface. The disc is released and slides downward along the surface of the cavity. Find the normal force acting on the block from the floor at the moment the disc is at the bottom of the cavity. Neglect friction between all surfaces.

We received many solutions to our September Challenge, The Second Half of the Flight. Unfortunately, very few of them came from students. We hope that our readers will keep encouraging their students to participate.

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