杏吧原创

#13 Snail party

Sam has four pet snails. She puts one of them at each corner of a square ABCD with sides 2 metres long. Being very friendly, each snail moves towards its neighbour, snail A to snail B, B to C, and so on, at all times pointing directly towards that neighbour. If each snail moves at a constant speed of 2 metres per hour, how long will it be before they meet?

Answer next week

#11 Lunar years

Solution

When I am 60, my sister on the moon will have just celebrated her 31st birthday.

The moon has a synchronous orbit. This means it takes the same amount of time to complete a full rotation in relation to the sun as it does to orbit Earth 鈥� 29.5 days. And the same side of the moon always faces us. So if my sister set up house in the Sea of Tranquility we could actually wave to her every night.

Her 鈥渄ay鈥� will be 29.5 of my Earth days. This means that 365 days or one year for her is equivalent to 29.5 of my years.

#12 Hole of the moon

Solution

The moon is about 350,000 kilometres away. The exact distance depends on the time of year because the moon moves on an elliptical orbit.

The moon is 3500 km across, and fills a hole 6 millimetres across at 鈥渁rm鈥檚 length鈥� of, say, 600 millimetres.

So by similar triangles, the distance to the moon is (600/6) x 3500, which equates to 350,000 km.

Quick Quiz #12

1 Hydra, Kerberos, Nix and Styx are to be found where in the solar system?

2 Shor鈥檚 algorithm allows a quantum computer to perform which mathematical operation far faster than a classical computer?

3 With an estimated population of 24 billion, what is thought to be the most populous (mainly) land vertebrate?

4 What cataclysm disturbed the peace of a Tuesday morning on 30 June 1908 near the Podkamennaya Tunguska river in Siberia?

5 Which condition results when a person inherits two abnormal copies of the haemoglobin gene, resulting in unusual red blood cells?

Answers below

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