A box contains three identical-looking marbles: one is solid lead, one is hollow copper, and one is solid wood. Without cutting them open, using scales, or submerging them in liquid, how can you identify which marble is which using a single flat wooden tabletop?
Roll them down a slope or across the table; their different weights and mass distributions will cause them to roll or stop uniquely.
Wait, let's look at a purely physical property: the lead marble is heavy, the wood is light, the copper is hollow. By rolling them, the lead marble has high momentum, the wood stops quickly due to low mass, and the hollow copper has a different center of mass behavior. Alternatively, spin them: the hard-boiled egg riddle style doesn't apply here. Let's use momentum and weight distribution: rolling them reveals their internal composition instantly because lead is heavy and dense, wood is light, and hollow copper has a shell distribution.
About this riddle
Logic riddles give you a few facts and ask what must be true. List what you know, cross out what cannot be, and see what is left.
Difficulty: Hard. More like this: Logic riddles with answers or try Einstein's Logic Grid for a different kind of puzzle.
More logic riddles
Three boxes are placed on a table. One contains gold, one contains silver, and one is empty. Each box has a statement written on it, but only one statement is true: - Box 1 (Gold box): 'The gold is in this box.' - Box 2 (Silver box): 'The gold is not in this box.' - Box 3 (Empty box): 'The silver is in Box 2.' Which box contains the gold?
Five runners finish a school marathon, and only these facts survive. Nico finished ahead of Iris. Carmen finished ahead of Hugo. Gwen finished ahead of Nico. Hugo finished ahead of Gwen. Who finished third?
Five runners finish a school marathon, and only these facts survive. Gwen finished ahead of Luca. Nico finished ahead of Boris. Luca finished ahead of Nico. Boris finished ahead of Pavel. Who finished second?
I possess a golden face and two long arms, but I have no hands to clap and no voice to call out the hours. What am I?
An electric train is traveling due north at 50 miles per hour, while the wind blows from the west at 20 miles per hour. In which direction does the smoke from the engine trail?
Five identical boxes are lined up in a row. A prize is hidden inside one of them. Box 1 is to the left of Box 2. Box 3 is to the right of Box 4. Box 5 is to the left of Box 1. Box 4 is to the left of Box 2. In which box is the prize?