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Riddles

Try to answer the below questions (without looking at hints before).

  • What is the water temperature at the bottom of an ocean or a deep lake? Assume surface air temperature at -20C.


  • Which is colder -25C or -25F? Which is colder -55C or -55F?


  • How many liters of water does the Earth have? Don’t need an exact number, just an order of magnitude.

    • (Hint: Solve it as a Fermi problem. Estimate a complex, seemingly unanswerable quantity using logical assumptions, known values and basic math)


  • We all know the Sun rises in the East and sets in the West. Which places on the Earth see the Sun rising from/setting in the North (or South) and when?


  • On Dec 21, 2020, Saturn and Jupiter appeared in the sky to have a conjunction. They were in the same sign/rashi. 

    • Saturn takes 30 years to go around the Sun, while Jupiter takes 12 years.

    • After how many years will they appear to be in the same sign again (not necessarily as close to have the conjunction we witnessed last December)? 

    • There are 2 possible answers although only one of them is possible in reality. What are the answers?

(Hint: Use angular speed and velocities to arrive at both the answers.)


  • On a fine day in June, I travel 10 kms North and then I travel 5 kms South. 

    • How far am I from my original location? 

    • I am not looking for the obvious answer of 5 kms North? What are the other answers?

(Hint: You can change the directions (go South first and then go North), but then you may want to change the month to December)


  • When a person is watching the lunar eclipse, his friend calls him and says that he is watching the Solar eclipse. 

    • How is this possible? Both of them are telling the truth.

    • It’s within the same 3 bodies (Sun, Moon and Earth)

(Hint: This type of conversation was not possible before 1969. Their third friend says that he is watching both the Solar and lunar eclipses).


  • Consider an object which is falling to the Earth from great heights. 

    • As it approaches the Earth, it experiences increasing gravity. 

    • Now imagine that the object falls into a hole after reaching the surface of the Earth. 

    • The hole is deep enough to reach the center of the Earth. 

    • Will the object continue to experience increasing gravity or a steady gravity or decreasing gravity? Explain your answer as to why.

(Hint: What will be the gravity at the center of the Earth?)


  • Derive a formula to calculate the length of the arc of Earth’s surface that a plane flying at a height of h will see.

(Hint: Use basic trigonometry)


  • Calculate the daylight hours for a given latitude on solstice. 

    • Extra credit - extend the formula to calculate on any day of the year (you can use days from solstice or equinox).

(Hint: Use basic trigonometry and make reasonable assumptions)


  • You may think of difference between an astrologer and astronomer as

    • Astrologer always tries to look in the future

    • Astronomers always try to look in the past, from the Big Bang to just 1 second in the past.

    • What is the significance of 1 second in the above statement?


  • Create the largest number out of 5, 7 and 8 using these numbers only once. Functions like factorials are not allowed.

    • (Hint: In general, if x and y are positive integers > 1 and x > y, which one will be larger x^y or y^x)

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