TEXT

The end of life on Earth?

It weighted about 10,000 tons, entered the atmosphere at a speed of 64,000 km/h and exploded over a city with a blast of 500 kilotons. But on 15 February 2013, we were lucky. The metereorite that showered pieces of rock over Chelyabinsk, Russia, was relatively small, at only about 17 metres wide. Although many people were injured by falling glass, the damage was nothing compared to what had happened in Siberia nearly one hundred years ago, when a relatively small object (approximately 50 metres in diameter) exploded in mid-air over a forest region, flattening about 80 million trees. If it had exploded over a city such as Moscow or London, millions of people would have been killed.

By a strange coincidence, the same day that the meteorite terrified the people of Chelyabinsk, another 50m-wide asteroid passed relatively close to Earth. Scientists were expecting that visit and know that the asteroid will return to fly close by us in 2046, but the Russian meteorite earlier in the day had been too small for anyone to spot.

Most scientists agree that comets and asteroids pose the biggest natural threat to human existence. It was probably a large asteroid or comet colliding with Earth which wiped out the dinosaurs about 65 million years ago. An enormous object, 10 to 16 km in diameter, struck the Yucatan region in Mexico with the force of 100 megatons. That is the equivalent of one Hiroshima bomb for every person alive on Earth today.

Many scientists, including the late Stephen Hawking, say that any comet or asteroid greater than 20km in diameter that hits Earth will result in the complete destruction of complex life, including all animals and most plants. As we have seen even a much smaller asteroid can cause great damage.

The Earth has been kept fairly safe for the last 65 million years by good fortune and the massive gravitational field of the planet Jupiter. Our cosmic guardian, with its stable circular orbit far from the sun, sweeps up and scatters away most of the dangerous comets and asteroids which might cross Earth’s orbit.

After the Chelyabinsk meteorite, scientists are now monitoring potential hazards even more carefully but, as far as they know, there is no danger in the foreseeable future.

Types of space rocks

• Comet – a ball of rock and ice that sends out a tail of gas and dust behind it. Bright comets only appear in our visible night sky about once every ten years.

• Asteroid – a rock a few feet to several kms in diameter. Unlike comets, asteroids have no tail. Most are to small to cause any damage and burn up in the atmosphere.

• Meteoroid – part of an asteroid or comet.

• Meteorite – what a meteoroid is called when it hits Earth.

Taken from: http://learningenglishteens.britishcouncil.org

- Access on 29/06/2020

The passage “the damage was nothing compared to what had happened in Siberia nearly one hundred years ago” states that the incident occurred a century ago.

TEXT

The end of life on Earth?

It weighted about 10,000 tons, entered the atmosphere at a speed of 64,000 km/h and exploded over a city with a blast of 500 kilotons. But on 15 February 2013, we were lucky. The metereorite that showered pieces of rock over Chelyabinsk, Russia, was relatively small, at only about 17 metres wide. Although many people were injured by falling glass, the damage was nothing compared to what had happened in Siberia nearly one hundred years ago, when a relatively small object (approximately 50 metres in diameter) exploded in mid-air over a forest region, flattening about 80 million trees. If it had exploded over a city such as Moscow or London, millions of people would have been killed.

By a strange coincidence, the same day that the meteorite terrified the people of Chelyabinsk, another 50m-wide asteroid passed relatively close to Earth. Scientists were expecting that visit and know that the asteroid will return to fly close by us in 2046, but the Russian meteorite earlier in the day had been too small for anyone to spot.

Most scientists agree that comets and asteroids pose the biggest natural threat to human existence. It was probably a large asteroid or comet colliding with Earth which wiped out the dinosaurs about 65 million years ago. An enormous object, 10 to 16 km in diameter, struck the Yucatan region in Mexico with the force of 100 megatons. That is the equivalent of one Hiroshima bomb for every person alive on Earth today.

Many scientists, including the late Stephen Hawking, say that any comet or asteroid greater than 20km in diameter that hits Earth will result in the complete destruction of complex life, including all animals and most plants. As we have seen even a much smaller asteroid can cause great damage.

The Earth has been kept fairly safe for the last 65 million years by good fortune and the massive gravitational field of the planet Jupiter. Our cosmic guardian, with its stable circular orbit far from the sun, sweeps up and scatters away most of the dangerous comets and asteroids which might cross Earth’s orbit.

After the Chelyabinsk meteorite, scientists are now monitoring potential hazards even more carefully but, as far as they know, there is no danger in the foreseeable future.

Types of space rocks

• Comet – a ball of rock and ice that sends out a tail of gas and dust behind it. Bright comets only appear in our visible night sky about once every ten years.

• Asteroid – a rock a few feet to several kms in diameter. Unlike comets, asteroids have no tail. Most are to small to cause any damage and burn up in the atmosphere.

• Meteoroid – part of an asteroid or comet.

• Meteorite – what a meteoroid is called when it hits Earth.

Taken from: http://learningenglishteens.britishcouncil.org

- Access on 29/06/2020

The damage caused by the Russian meteorite

TEXT

The end of life on Earth?

It weighted about 10,000 tons, entered the atmosphere at a speed of 64,000 km/h and exploded over a city with a blast of 500 kilotons. But on 15 February 2013, we were lucky. The metereorite that showered pieces of rock over Chelyabinsk, Russia, was relatively small, at only about 17 metres wide. Although many people were injured by falling glass, the damage was nothing compared to what had happened in Siberia nearly one hundred years ago, when a relatively small object (approximately 50 metres in diameter) exploded in mid-air over a forest region, flattening about 80 million trees. If it had exploded over a city such as Moscow or London, millions of people would have been killed.

By a strange coincidence, the same day that the meteorite terrified the people of Chelyabinsk, another 50m-wide asteroid passed relatively close to Earth. Scientists were expecting that visit and know that the asteroid will return to fly close by us in 2046, but the Russian meteorite earlier in the day had been too small for anyone to spot.

Most scientists agree that comets and asteroids pose the biggest natural threat to human existence. It was probably a large asteroid or comet colliding with Earth which wiped out the dinosaurs about 65 million years ago. An enormous object, 10 to 16 km in diameter, struck the Yucatan region in Mexico with the force of 100 megatons. That is the equivalent of one Hiroshima bomb for every person alive on Earth today.

Many scientists, including the late Stephen Hawking, say that any comet or asteroid greater than 20km in diameter that hits Earth will result in the complete destruction of complex life, including all animals and most plants. As we have seen even a much smaller asteroid can cause great damage.

The Earth has been kept fairly safe for the last 65 million years by good fortune and the massive gravitational field of the planet Jupiter. Our cosmic guardian, with its stable circular orbit far from the sun, sweeps up and scatters away most of the dangerous comets and asteroids which might cross Earth’s orbit.

After the Chelyabinsk meteorite, scientists are now monitoring potential hazards even more carefully but, as far as they know, there is no danger in the foreseeable future.

Types of space rocks

• Comet – a ball of rock and ice that sends out a tail of gas and dust behind it. Bright comets only appear in our visible night sky about once every ten years.

• Asteroid – a rock a few feet to several kms in diameter. Unlike comets, asteroids have no tail. Most are to small to cause any damage and burn up in the atmosphere.

• Meteoroid – part of an asteroid or comet.

• Meteorite – what a meteoroid is called when it hits Earth.

Taken from: http://learningenglishteens.britishcouncil.org

- Access on 29/06/2020

In the sentence “the dangerous comets and asteroids which might cross Earth’s orbit”, the underlined word is similar to

No circuito abaixo, a bateria possui fem igual a !$ ε !$ e resistência interna r constante e a lâmpada incandescente L apresenta resistência elétrica ôhmica igual a 2r. O reostato R tem resistência elétrica variável entre os valores 2r e 4r.

Ao deslocar o cursor C do reostato de A até B, verifica-se que o brilho de L

O polinômio de raízes reais distintas e coeficientes reais, !$ P(x) = 6x^3 + mx^2 - 18x + n !$, é divisível por !$ (x - \alpha) !$ e possui duas raízes simétricas.

Se !$ P(P(\alpha)) = 9 !$, então !$ P(1) !$ é igual a

Considere um circuito ôhmico com capacitância e auto-indução desprezíveis. Através de uma superfície fixa delimitada por este circuito (Figura 1) aplica-se um campo magnético !$ \vec B !$ cuja intensidade varia no tempo t de acordo com o gráfico mostrado na Figura 2.

Nessas condições, a corrente induzida i no circuito esquematizado na Figura 1, em função do tempo t, é melhor representada pelo gráfico

O ozônio (O₃) é naturalmente destruído na estratosfera superior pela radiação proveniente do Sol.

Para cada molécula de ozônio que é destruída, um átomo de oxigênio (O) e uma molécula de oxigênio (O₂) são formadas, conforme representado abaixo:

Sabendo-se que a energia de ligação entre o átomo de oxigênio e a molécula O₂ tem módulo igual a 3,75 eV, então o comprimento de onda dos fótons da radiação necessária para quebrar uma ligação do ozônio e formar uma molécula O₂ e um átomo de oxigênio vale, em nm,

Considere no plano de Argand Gauss os números complexos z = x + yi , em que x e y são números reais e !$ \sqrt {- 1} = i !$ tais que

!$ \begin{cases} |z + i| = 5 \\ Im(z) + z^2 + |\bar z|^2 - Re(z) . \left[Re(z) + 2 . \left (i^{1093}\right) . Im(z)\right] = 12 \end{cases} !$

É correto afirmar que os pontos P(x, y) , afixos de z, podem formar um

TEXT

The end of life on Earth?

It weighted about 10,000 tons, entered the atmosphere at a speed of 64,000 km/h and exploded over a city with a blast of 500 kilotons. But on 15 February 2013, we were lucky. The metereorite that showered pieces of rock!$ ^{A)} !$ over Chelyabinsk, Russia, was relatively small, at only about 17 metres wide. Although many people were injured by falling glass, the damage was nothing compared to what had happened in Siberia nearly one hundred years ago, when a relatively small object (approximately 50 metres in diameter) exploded in mid-air over a forest region, flattening about 80 million trees. If it had exploded over a city such as Moscow or London, millions of people would have been killed.

By a strange coincidence, the same day that the meteorite!$ ^{B)} !$ terrified the people of Chelyabinsk, another 50m-wide asteroid passed relatively close to Earth. Scientists were expecting that visit and know that the asteroid will return to fly close by us in 2046, but the Russian meteorite earlier in the day had been too small for anyone to spot.

Most scientists agree that comets and asteroids pose the biggest natural threat to human existence. It was probably a large asteroid or comet colliding with Earth which wiped out the dinosaurs about 65 million years ago. An enormous object, 10 to 16 km in diameter, struck the Yucatan region in Mexico with the force of 100 megatons. That is the equivalent of one Hiroshima bomb!$ ^{C)} !$ for every person alive on Earth today.

Many scientists, including the late Stephen Hawking, say that any comet or asteroid greater than 20km in diameter that hits Earth!$ ^{D)} !$ will result in the complete destruction of complex life, including all animals and most plants. As we have seen even a much smaller asteroid can cause great damage.

The Earth has been kept fairly safe for the last 65 million years by good fortune and the massive gravitational field of the planet Jupiter. Our cosmic guardian, with its stable circular orbit far from the sun, sweeps up and scatters away most of the dangerous comets and asteroids which might cross Earth’s orbit.

After the Chelyabinsk meteorite, scientists are now monitoring potential hazards even more carefully but, as far as they know, there is no danger in the foreseeable future.

Types of space rocks

• Comet – a ball of rock and ice that sends out a tail of gas and dust behind it. Bright comets only appear in our visible night sky about once every ten years.

• Asteroid – a rock a few feet to several kms in diameter. Unlike comets, asteroids have no tail. Most are to small to cause any damage and burn up in the atmosphere.

• Meteoroid – part of an asteroid or comet.

• Meteorite – what a meteoroid is called when it hits Earth.

Taken from: http://learningenglishteens.britishcouncil.org

- Access on 29/06/2020

In “scientists were expecting that visit”, the underlined word has the same use as in

A partir do instante t₀ = 0, uma partícula com velocidade inicial v₀ é uniformemente acelerada.

No instante t, a aceleração cessa e a partícula passa a se movimentar com velocidade constante v. Do instante 2t ao instante 4t, uma nova aceleração constante atua sobre a partícula, de tal forma que, ao final desse intervalo, sua velocidade vale -v.

Nessas condições, a velocidade média da partícula, no intervalo de 0 a 4t, é igual a