Một vật dao động điều hòa với biên độ A và tốc độ cực đại V m a x . Chu kỳ dao động của vật là:

A.  T = v max A

B.  T = A v max

C.  T = v max 2 π A

D.  T = 2 π A v max

Độ to của âm liên quan đến đặc trưng vật lí nào của âm ?

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 67 to 76.

Ralph Earl was born into a Connecticut farm family in 1751. He chose early to become a painter and looked for what training was available in his home state an in Boston. Earl was one of the first American artists to paint landscapes. Among his first paintings were scenes from the Revolutionary war battles of Lexington and Concord In 1778 Earl went to London to study with Benjamin West for four years.

When Earl returned to the United States, he was jailed for fourteen months for outstanding debts. While still a prisoner, he painted portraits of some of New York City's most elegant society women and their husbands. After his release, he took up the trade of itinerant portrait painter, working his way through southern New England and New York. He didn't flatter his subjects, but his portrait show a deep understanding of them; perhaps he had sprung from the same roots.

Among Earl's most famous paintings is his portrait of Justice Oliver Ellsworth and his wife, Abigail. To provide counterpoint to the severity of the couple, he accurately details the relative luxury of the Ellsworth's interior furnishings. The view through the window behind them shows sun lit fields, well-kept fences, and a bend of the Connecticut River. One of Earl's paintings is something of anomaly. Reclining Hunter, which many years was attributed to Thomas Gainsborough, shows a well-dressed gentleman resting beneath a tree. In the foreground, he displays a pile of birds, the results of a day's hunt. The viewer can also see a farmer's donkey lying in the ground, another of the hunter's victims. This outrageously funny portrait couldn't have been commissioned - no one would have wanted to be portrayed in such an absurd way. However, this painting uncharacteristically shows Earl's wit as well as his uncommon technical skills.

Which of the following could be substituted for outstanding without changing the meaning of the sentence?

A. excellent

B. unpaid

C. illegal

D. shocking

Độ cao của âm là gì? Nó có liên quan đến đặc trưng vật lí nào của âm ?

Cho các chất hữu cơ: X, Y là hai ancol có cùng số nguyên tử cacbon trong phân tử, Z là axit no, mạch hở (M_Z > 90) và este T (phân tử chỉ chứa chức este) tạo bởi X, Y với một phân tử Z. Đốt cháy hoàn toàn 0,325 mol hỗn hợp E gồm X, Y, Z và T, thu được 20,16 lít CO₂ (đktc) và 17,55 gam H₂O. Phần trăm số mol của T trong E gần nhất với giá trị nào sau đây? 

A. 7,75. 

B. 7,70

C. 7,85. 

D. 7,80

Read the following passage and mark the letter A, B, C or B on your answer sheet to indicate the correct answer to each of the questions from 30 to 37.

  Many ants forage across the countryside in large numbers and undertake mass migrations; these activities proceed because one ant lays a trail on the ground for the others to follow. As a worker ant returns home after finding a source of food, it marks the route Line by intermittently touching its stinger to the ground and depositing a tiny amount of trail pheromone – a mixture of chemicals that delivers diverse messages as the context changes.

  These trails incorporate no directional information and may be followed by other ants in either direction. Unlike some other messages, such as the one arising from a dead ant, a food trail has to be kept secret from members of other species. It is not surprising then that ant species use a wide variety of compounds as trail pheromones. Ants can be extremely sensitive to these signals. Investigators working with the trail pheromone of the leafcutter ant Atta texana calculated that one milligram of this substance would suffice to lead a column of ants three times around Earth. The vapor of the evaporating pheromone over the trail guides an ant along the way,  and the ant detects this signal with receptors in its antennae. A trail pheromone will evaporate to furnish the highest concentration of vapor right over the trail, in what is called a vapor space. In following the trail, the ant moves to the right and left, oscillating from side to side across the line of the trail itself, bringing first one and then the other antenna into the vapor space. As the ant moves to the right, its left antenna arrives in the vapor space. The signal it receives causes it to swing to the left, and the ant then pursues this new course until its right antenna reaches the vapor space. It then swings back to the right, and so weaves back and forth down the trail.

What does the passage mainly discuss?

A. The mass migration of ants

B. How ants mark and follow a chemical trail 

C. Different species of ants around the world 

D. The information contained in pheromones

Every year, millions of people descend _____ protected and pristine natural areas to observe rare species.

A. on

B. at 

C. in 

D. to

Hãy kể ra những đặc trưng sinh lí của âm

Để điều chế K kim loại người ta có thể dùng các phương pháp sau:

(1) Điện phân dung dịch KCl có vách ngăn xốp.

(2) Điện phân KCl nóng chảy.

(3) Dùng Li để khử K ra khỏi dd KCl.

(4) Dùng CO để khử K ra khỏi K₂O.

(5) Điện phân nóng chảy KOH.

Chọn phương pháp thích hợp:

A. Chỉ có 1, 2

B. Chỉ có 2, 5

C. Chỉ có 3, 4, 5

D. 1, 2, 3, 4, 5