Todas as questões do ENEM

      It’s a perilous time to be a statue. Not that it has ever been a particularly secure occupation, exposed as statues are to the elements, bird droppings and political winds.

      Just ask Queen Victoria, whose rounded frame perches atop hundreds of plinths across the Commonwealth, with an air of solemn, severe solidity. But in 1963 in Quebec, members of a separatist paramilitary group stuck dynamite under the dress of her local statue. It exploded with a force so great that her head was found 100 yards away.

      Today, the head is on display in a museum, with her body preserved in a room some miles away. The art historian Vincent Giguère said that “the fact it’s damaged is what makes it so important.”

      There’s another reason to conserve the beheaded Victoria. Statues of women, standing alone and demanding attention in a public space, are extremely rare.

      To be made a statue, a woman had to be a naked muse, royalty or the mother of God. Or occasionally, an icon of war, justice or virtue: Boadicea in her chariot in London, the Statue of Liberty in New York.

      Still, of 925 public statues in Britain, only 158 are women standing on their own. Of those, 110 are allegorical or mythical, and 29 are of Queen Victoria.

                                                         Julia Baird, The New York Times. September 4, 2017. Adaptado. 

Examine as estruturas do ortocresol e do álcool benzílico.

O ortocresol e o álcool benzílico

      Algorithms are everywhere. They play the stockmarket, decide whether you can have a mortgage and may one day drive your car for you. They search the internet when commanded, stick carefully chosen advertisements into the sites you visit and decide what prices to show you in online shops. (…) But what exactly are algorithms, and what makes them so powerful?

      An algorithm is, essentially, a brainless way of doing clever things. It is a set of precise steps that need no great mental effort to follow but which, if obeyed exactly and mechanically, will lead to some desirable outcome. Long division and column addition are examples that everyone is familiar with — if you follow the procedure, you are guaranteed to get the right answer. So is the strategy, rediscovered thousands of times every year by schoolchildren bored with learning mathematical algorithms, for playing a perfect game of noughts and crosses. The brainlessness is key: each step should be as simple and as free from ambiguity as possible. Cooking recipes and driving directions are algorithms of a sort. But instructions like “stew the meat until tender” or “it’s a few miles down the road” are too vague to follow without at least some interpretation.

      (…)

                                                                                                          The Economist, August 30, 2017.

      Algorithms are everywhere. They play the stockmarket, decide whether you can have a mortgage and may one day drive your car for you. They search the internet when commanded, stick carefully chosen advertisements into the sites you visit and decide what prices to show you in online shops. (…) But what exactly are algorithms, and what makes them so powerful?

      An algorithm is, essentially, a brainless way of doing clever things. It is a set of precise steps that need no great mental effort to follow but which, if obeyed exactly and mechanically, will lead to some desirable outcome. Long division and column addition are examples that everyone is familiar with — if you follow the procedure, you are guaranteed to get the right answer. So is the strategy, rediscovered thousands of times every year by schoolchildren bored with learning mathematical algorithms, for playing a perfect game of noughts and crosses. The brainlessness is key: each step should be as simple and as free from ambiguity as possible. Cooking recipes and driving directions are algorithms of a sort. But instructions like “stew the meat until tender” or “it’s a few miles down the road” are too vague to follow without at least some interpretation.

      (…)

                                                                                                          The Economist, August 30, 2017.

Uma minicama elástica é constituída por uma superfície elástica presa a um aro lateral por 32 molas idênticas, como mostra a figura. Quando uma pessoa salta sobre esta minicama, transfere para ela uma quantidade de energia que é absorvida pela superfície elástica e pelas molas.

Considere que, ao saltar sobre uma dessas minicamas, uma pessoa transfira para ela uma quantidade de energia igual a 160 J, que 45% dessa energia seja distribuída igualmente entre as 32 molas e que cada uma delas se distenda 3,0 mm. Nessa situação, a constante elástica de cada mola, em N/m, vale

A figura mostra a trajetória de um projétil lançado obliquamente e cinco pontos equidistantes entre si e localizados sobre o solo horizontal. Os pontos e a trajetória do projétil estão em um mesmo plano vertical.

No instante em que atingiu o ponto mais alto da trajetória, o projétil explodiu, dividindo-se em dois fragmentos, A e B, de massas MA e MB, respectivamente, tal que MA = 2MB. Desprezando a resistência do ar e considerando que a velocidade do projétil imediatamente antes da explosão era VH e que, imediatamente após a explosão, o fragmento B adquiriu velocidade VB = 5VH, com mesma direção e sentido de VH, o fragmento A atingiu o solo no ponto