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This quiz will test your knowledge and understanding of Physics topic 1.1.
Questions and Answers
1.
Earth's mass is about kg. Please estimate the number of atoms in the entire Earth.
A.
B.
C.
D.
E.
Correct Answer C.
Explanation 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.
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2.
Earth's radius is about 6378km. Please estimate the number of atoms in Earth.
A.
B.
C.
D.
E.
Correct Answer C.
Explanation 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.
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3.
Please estimate how many times on average a human heart beats in a human's life time, assuming that the average person lives for 75 years and that the heart beats between 60 and 80 times per minute.
A.
B.
C.
D.
E.
Correct Answer B.
Explanation The number of heartbeats in a human's lifetime is heartbeats/min min/hr hr/day days/year years heartbeats.
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4.
Please calculate the thickness of a piece of paper in millimeters, assuming the thinkness of a 500-page book to be 5 cm.
A.
B.
C.
D.
E.
Correct Answer C.
Explanation The thickness of a piece of paper is .
Pay attention to the units. It is 0.0001 in meters. But answer E is wrong.
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5.
What is the ratio of the age of the universe to the time it takes for the traffic light to change from red to green, assuming that the age of universe is 14 billion years and the waiting time for the light change is 1 minute?
A.
B.
C.
D.
E.
Correct Answer C.
Explanation 14 billion years years days/year hr/day sec/min seconds.
The ratio is