One Good Turn

Seen one of those plastic lawn sprinklers? You know, the ones that go round and round at one end spraying water on the grass and are connected to a tap at the distant end, with a long pipe in between

E4

The following “thought puzzle” is attributed to the great late polymath Nobel Laureate, the American physicist Richard Feynman, of the famous Feynman Lectures on Physics fame who, incidentally also knew how to pick a lock when he wasn’t being futuristic and introducing concepts like nanotechnology light years ahead of its time. It’s said that he just toyed with the following fascinating puzzle without ever giving a solution. You don’t need to either, but try all the same:

Seen one of those plastic lawn sprinklers? You know, the ones that go round and round at one end spraying water on the grass and are connected to a tap at the distant end, with a long pipe in between. Well, what would happen if we took the whole assembly minus the tap, immersed it underwater in a swimming pool and then sucked on the tap end of the pipe (ourselves being underwater too, of course)? Would the sprinkler end rotate? And if it did would it do so in the same direction as before? Or anti?

However, as far as real puzzles go, here’s one. A boy of 10 years entered the northernmost point of a circular jungle park of 10 miles diameter. Proceeding due south for 3 miles, he found a monument. From there, he went due west until he reached the edge of the park. From that point, he went due south for 2 miles and found another monument. He could easily find the distance between the two monuments. How? But wait, do not try with Pythagoras theorem, for, the boy himself was the young Pythagoras, who formulated his theorem at a later stage only — Sheikh Sintha Mathar, sheikhsm7@gmail.com

DEAR MS

(A few months back we had run the following problem: “The annoying thing about mosquitoes is that they often buzz exactly around our ears before biting. How can they identify our ears even in the darkness?” It had generated a lot of responses, several of which were correct. However there were a few interesting alternate takes that were not run but whose time has probably come because they bring out another facet of the problem. — MS)

The-Latest-Buzz-Dept:

When the sound waves hit the eardrum, it vibrates. Mosquitoes are able to sense these vibrations. Thus, they are able to identify our ears even in darkness.

• Prisca Susan Mathew, priscasmathew@gmail.com

Carbon dioxide attracts mosquitoes because they have a special kind of receptor to sense it. Therefore, they get drawn to our face.

• Navaneeth Rajan, navaneethrajan@yahoo.com

Mosquitoes have a strong sense of smell and can sniff their way in the dark. And besides, they are attracted to substances like earwax and sweat, which makes identification of ears easier.

• Iqra Zafar, iqra1849@gmail.com

(The problem was: “What is the next number in the series: 1, 1 1, 2 1, 1 2 1 1, 1 1 1 2 2 1, ? — MS)

Once-Two-Many-Dept:

In the given sequence every succeeding number describes the number preceding it. For example the first number is 1, so the second number describes it as “one 1”. Similarly the third number describes the second number as “two 1’s” and so on. According to this pattern, the number following 111221 must be 312211 (“three 1’s, two 2’s and one 1”)

• Vivek Prinse John, vivekprinsejohn@gmail.com (Yes, Athiyaman at athinalla@gmail.com, you got that right too. — MS)

Semi-SPHERE-DEPT:

Regarding the two sphere problem, the radius of the smaller sphere has got to be 0.17 m or 17 cm. I got it by simple geometry and then by drawing an incircle in the triangle enclosed within the two vertical walls and the circle (when viewed from the top).

• Arpan, 2998b2nayak2998@gmail.com

ENDGAME

When you light a gas stove why doesn’t the flame travel from the burner to the cylinder via the pipe and instead stays only at the burner?

(To get in touch with Mukul, mail him at mukul.mindsport@gmail.com)

• Mindsport