Answer to Question #97294 in Mechanics | Relativity for nesha

Question

There are two identical shoe boxes on a table. You friend has put a brick in one of them. Describe how you could use one of Newton's laws to figure out which box is more massive without picking them up, or opening them, or using a scale.

Answer 1

I would set the boxes in motion on the surface, pushing them. The coefficient of sliding friction of the boxes is the same, but the friction force is directly related to the weight of the box. With uniform motion, the force I applied should be equal to the friction force, where a large force is required - there is a brick.