Physics 1.1 - The Realm Of Physics

Earth's radius is about  m. Each atom is about m.



It takes  =  atoms to be as long as Earth's radius. Since Earth is three-dimensional, it should contain = atoms.

If you forgot to convert the unit from kilometers to meters, you will end up with the wrong answer B.

The mass of Earth is about  kg =  g.

Suppose all this mass is made up by the lightest molecule, hydrogen, which is 2 g/mol. Then there would be  mol. Each mole will contain kg of molecules. So the number of hydrogen molecules in  kg would be equal to  mol/ mol . Each hydrogen molecule contains two hydrogen atoms, so the number of atoms would be of order . This gives us an upper limit.

 

Suppose all this mass is made up by some heavy element, say iron, which is 56 g/mol. Then there would be about mol. Each mole again contains  iron atoms. So the number of iron atoms equals to  mol / mol . This gives us a lower limit. So C should be the right answer.

 

If you forget to convert kilograms to grams, you might choose the wrong answer B.

 

The thickness of a piece of paper is  .

Pay attention to the units. It is 0.0001 in meters. But answer E is wrong.

The number of heartbeats in a human's lifetime is  heartbeats/min  min/hr  hr/day days/year  years heartbeats.

14 billion years years  days/year  hr/day  sec/min  seconds. 

The ratio is