IB Physics Galileo's Dying Breath

A tutorial sheet of estimation questions is given below.

1. Estimate how many molecules of air exhaled by Galileo during his dying breath you are likely to breathe during one breath. Surface area of the Earth = 5x10⁸ km².
2. Estimate the time taken by a ray of light to travel the diameter of a hydrogen atom.
3. Estimate the number of oxygen molecules in the air in a science laboratory.
4. Estimate the number of atoms in a grain of sand.
5. (After Enrico Fermi) Estimate the number of piano tuners in Chicago.
6. Enrico Fermi was 10 miles from the blast site of the first atomic bomb. He released pieces of paper from rest and found that they travelled 2.5 m as the blast wave passed. Estimate the energy released in the blast. 1 ton of TNT yields 4x10⁹ J of energy. [equivalent to 10 kilotons of TNT]