Re-entry level question ...... don’t space out!

The following question was posed in this column hundreds of weeks back: “When a spacecraft re-enters the Earth’s atmosphere its surface gets extremely hot due to friction with air particles.

Published: 09th September 2017 10:00 PM  |   Last Updated: 09th September 2017 04:17 PM   |  A+A-

The following question was posed in this column hundreds of weeks back: “When a spacecraft re-enters the Earth’s atmosphere its surface gets extremely hot due to friction with air particles. Why doesn’t the same thing happen when it’s initially launched?”

What ignited the problem was that many people apparently answered correctly saying something like when a rocket is launched its initial velocity is not all that great even though it is accelerating tremendously. Also, by the time its speed reaches anywhere near that which could cause air friction, the air itself has begun to thin out.

But what finally compounded that ignition was blissful ignorance. Therefore this re-run. Meaning don’t answer the question this time; just tell us what’s wrong with it.

Throughput
(The cold case was: “A chain of length L cm and mass M kg is suspended vertically by one end with the other end above a scale. The chain is released and falls. At the instant the entire chain has fallen onto the scale what does the scale read?”)

As the chain is falling freely under gravity so at any instant t after the chain is released, when its free end goes down by x, the speed v of the chain is given as v = sqrt2gx. In further small interval of etc etc etc . . . Hence the total force the chain exerts on the scale when it comes down a length x is (Mv2/L + Mgx/L) or 3Mgx/L as v = sqrt2gx. In other words when the chain falls by a length x, the scale reads 3Mx/L. So when the chain falls a length L, the scale reads 3M. -- Shashi Shekher Thakur, shashishekher@yahoo.com

(The second problem was: “Solve the number series by identifying the last number. 1, 4, 5, 6, 7, 9, 11, ?”)

I wrote down the numbers in words and tried to see a pattern. Lo and behold! T seems to be the culprit. All the numbers listed do not have the alphabet T when written. But the next number 100 is a bit further away! I am aware that the numbers 1 to 100 do not contain A, B or C but I didn’t know that T would give them a tough competition. -- Saishankar Swaminathan, saishankar482@gmail.com
If the above numerals are spelt, none of them have the letter T in it. Since all the numerals from 12 to 99 contain T when spelt, the next number without T is 100. -- Palicherlu V Prakash, pvprakaash@gmail.com

(The third one was: “Tony says his grandfather who fought in World War I was so brave that he was awarded a medal with the words “For our Courageous Soldiers In World War I” embedded. Bill knows that his friend is lying. How?”)

How did the people who awarded the medal know that there was to be a WWII?
This is like the coin with the inscription 10 BC found by an archaeologist. It had to be a fake for those who minted it could not have known that Jesus Christ was to be born 10 years later and that time would be counted from his year of birth! And then again there’s an issue for how people believe that he was born three years before or 3 BC! -- Ajit Athle, ajitathle@gmail.com
The term World War I was coined in the year 1939. So when Tony’s grandfather received the award he wouldn’t know that it was WW1. Thus Bill knew that he was lying. -- Advaith Ram Ravichandran, advaithbarca@gmail.com

In case you publish this, please DO publish my email ID so that I can get the email IDs of all the evildoers who exploit other people’s email IDs and compile and send them to you. What do you say? (Do that Jimbo! -- MS) -- Jimmy Evil, rubcjazz@gmail.com
(Also among the first five are: Wg Cdr Raju Srinivasan, rajusrinivasan@gmail.com; B B Agrawal, bbagrawal@yahoo.com; Hema Parthasarathy, hemapartha133@gmail.com; Vijayalakshmi Sudheer, vijisudheer62@gmail.com; Prajwal Paramjyoti, paramprajwal.b@gmail.com)

1. A person steals wine by removing three cups of wine from a barrel and replacing it with three cups of water. The next day also he does the same thing with the now diluted wine.  The following day he repeats it again. In all, he has drawn three times from the same barrel and has poured back nine cups of water. At this point the barrel is 50% wine and 50% water. How many cups of wine were there initially in the barrel? (Submitted by Dr P Gnanaseharan, gnanam.chithrabanu@gmail.com
2. Why are the bones of tinned fish almost as soft as the flesh?

Mukul Sharma

Sharma is a scriptwriter and former editor of Science Today magazine.(mukul.mindsport@gmail.com)

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