#45 Beetles on a clothes line
Peg beetles are a rare species with rather odd behaviour. As any peg beetle expert will know, these beetles always walk at 1 metre per minute, and when two beetles meet, they immediately reverse direction.
Six peg beetles are on a 2-metre-long clothes line, some walking left to right and others right to left (as the diagram shows). As we join the action, beetle A is at the left-hand end of the line and walking towards the right, while beetle F is at the right-hand end, walking left.
When a beetle reaches the end of the clothes line, it drops off onto the ground.
Which two beetles will be the last to drop off the clothes line, and how long will it be before that happens?
Answer next week
#44 Elevator pitch
Solution
In a lift accelerating upwards, neither the helium balloon nor the ice cube move at all. The spider does move down, however.
Anything floating, as Archimedes postulated, is subject to an upwards buoyancy force equal to the weight of the displaced fluid. Gravity, as Einstein explained, cannot be distinguished from acceleration so everything feels heavier in the accelerating lift, including the water, ice cube, helium and air. The spider also feels heavier and so the silk it hangs from has to stretch, by Hooke鈥檚 law.
Quick quiz #37
1 Vitamins are organic micronutrients essential to the functioning of an organism鈥檚 metabolism. How many are humans generally considered to need?
2 Which vitamin, also known as cobalamin, is essential to the functioning of the nervous system and generally only found in animal-derived foods?
3 The synthesis of cholecalciferol in the skin on exposure to UVB radiation is one way humans acquire which vitamin?
4 Which disease, with effects on the cardiovascular and nervous systems, is associated with a deficiency of vitamin B1, or thiamine?
5 A spinach, red pepper, grapefruit and parsley smoothie would hugely boost your intake of which vitamin?
Answers below
Quick quiz #37
Answers
1 Thirteen: vitamins A, B1, B2, B3, B5, B6, B7, B9, B12, C, D, E and K
2 Vitamin B12
3 Vitamin D
4 Beriberi
5 Vitamin C. By mass, parsley has almost three times as much vitamin C as fresh orange juice
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