Opaque Marble Balls

Lost in the woods, you come upon a mysterious stranger who hands you two large spheres made of two kinds of opaque marble. The spheres look the same, are the same size and have the same weight and apparent density; however, one is solid and the other hollow. The hollow sphere contains a tiny map that will enable you to navigate your way home. Unfortunately, you cannot break the spheres. The stranger agrees to open the sphere that contains the map only if you can determine which sphere is hollow. How do you determine which sphere is hollow?

Answer
Roll the spheres on a level flat surface. The hollow sphere will roll further because its mass is distributed away from the centre giving it a higher moment of inertia. Alternatively, you could spin them and see which is harder to stop.

Leave a Comment

Your email address will not be published. Required fields are marked *

You cannot copy content of this page

×

Powered by WhatsApp Chat

× How can I help you?