An astronaut is floating in outer space. She needs to find her air tanks or she will be doomed. She only has time to unlock one of the three cases. She knows that the air tanks are in the most massive tank. How can she find out which case is the most massive? Weigh all of the cases using a scale.

Determine which case has the greatest volume by multiplying height x width x length.

Apply an equal amount of force to all three cases and see which has less acceleration.

It is impossible to tell which is which.