题目内容
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If a small circular current is placed in a uniform magnetic field, at which angle θ there will be maximum torque acting on the circular current？
A、0
B、π/4
C、π/2
D、π
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A small ball (m=50g) connected by a rope is moving on frictionless table circularly with ω =7rad/s and r=30cm. Then one pulls the rope slowly through the center. When the radius of circular motion reduces to r’=10cm, the work done on the ball is _____________J.
这个练习任务一共有四个段落，请你顺序阅读第一题到第四题，并且为每一个段落（对应一题）找到最恰当到subheading，并在做判断到时候体会前面视频中降到到subheading的重要性和写作技巧。 第一段：On a starlit night, beetles were released with their dung balls from the center of a circular arena of flattened and leveled sand, enclosed within a 1 m high, featureless circular wall. To determine how accurately dung beetles can orientate along straight paths when prevented from seeing any celestial cues, we obscured the dorsal visual fields of Scarabaeus satyrus with small cardboard caps (Figure 1C), whereas the ventral eyes were not impeded. … To test for a possible effect of the cap, we also fitted beetles with a transparent plastic cap of the same shape as the cardboard version. … Thus, the straight-line orientation of S. satyrus is significantly impaired if they are prevented from seeing the starlit sky.
A、Scarabaeus satyrus fails to orient without celestial clues
B、Scarabaeus satyrus uses stars of night sky for orientation
C、Scarabaeus satyrus uses milky way for orientation
D、Future experiments
Many, many centuries ago, large distances were measured in the Babylonian mile. The Babylonian mile equaled about seven of our miles. Because of its length, the time needed to travel the Babylonian mile became a measure of time. One day was said to be twelve Baby-Ionian time-miles.
About one thousand years before Christ, the Babylonians began keeping records of star movements. They needed a way to record how much time passed between the moment they first saw a star and then observed it again. They used the Babylonian time-mile as their measure of time.
In order to have small units of time, the Babylonians divided their time-mile into thirty parts. The Babylonians believed that each trip around the sky was a circle. One complete trip around the sky, they reasoned, took one day.
You already know that one day was the same as twelve Babylonian time-mile. Since each time-mile was divided into thirty parts, the circular trip around the sky was 12×30, or 360 parts long. That is how there came to be 360 4egrees in a circle.
The purpose of this passage is to explain ______.
A．how the Babylonians measured the time of star movements
B．why the circle is divided into 360 degrees
C．the Babylonian mile and the Babylonian time-mile
D．the Babylonians' ideas about the sky
The invention of coins appears to have occurred almost simultaneously but quite independently in ancient Greece and in China in about 800 BC. The reason historians believe development was independent is because of the notable differences in the two systems.
The first money to appear in China was made of bronze. More notably, it was not -circular, but in the shape of a knife ! The knife had a hole pierced in the handle so that it could be suspended (for example, from a string), and it generally bore an inscription. Other shapes included keys or spades, but what they had in common was the pierced hole. It was probably round 250 BC that the first Chinese money we would recognize as coins appeared, and, subsequently, the famous Ming mint produced a round coin with a square hole in it. This particular coin bore the inscription, "Knife of Ming", but the knife itself had disappeared. It was from this coin that the famous "cash" developed. The Chinese word, "cash" means "a small unit of currency". Al though Chinese coins often have inscriptions, they virtually never had portraits, or types of any kind, until the 19th century when they were influenced by western models.
It is implied in the passage that ______.
A．people used to prefer gold and silver as their medium of exchange
B．money was invented first in Europe and then in Asia
C．coins appeared as the result of inconvenience in exchange
D．the earliest coins were made quite differently from those we are using now
Most of the near side of the Moon was thoroughly mapped and studied from telescopic pictures years before the age of space exploration. Earth-based telescopes can resolve objects as small as a few hundred meters on the lunar surface. Close observation of craters, combined with the way the Moon diffusely reflects sunlight, led to the understanding that the Moon is covered by a surface layer, or regolith , that overlies the solid rock of the Moon. Telescopic images permitted the cataloging of a bewildering array of land forms. Craters were studied for clues to their origin; the large circular maria were mapper. Wispy marks on the surface (known as rays) emanating from certain craters were seen. Strange, sinuous features were observed in the maria. Although various land forms were catalogued, the majority of astronomers' attention was fixed on craters and their origins.
Astronomers have known for a fairly long time that the shape of craters changes as they increase in size. Small craters with diameters of less than lO-15km have relatively simple shapes. They have rim crests that are elevated above tile surrounding terrain, smooth, bowl-shaped interiors, and depths that are about one-fifth to one-sixth their diameters. The complexity of shape increases for larger craters.
What does the passage mainly discuss？
A．What astronomers learned from the Surveyor and Apollo space missions.
B．Characteristics of the major terrains of the Moon
C．The origin of the Moon's craters.
D．Techniques used to catalogue the Moon's land forms.
The Moon, which has undergone a distinct and complex geological history, presents a
striking appearance. The moon may be divided into two major terrains: the maria (dark
lowlands) and the terrace(bright highlands). The contrast in the reflectivity (the capability
of reflecting light) of these two terrains suggested to many early observers that the two
(5) terrains might have different compositions, and this supposition was confirmed by missions to
the Moon such as Surveyor and Apollo. One of the most obvious differences
between the terrains is the smoothness of the maria in contrast to the roughness of the
highlands. This roughness is mostly caused by the abundance of craters; the highlands are
completely covered by large craters(greater than 40-50 km in diameter), while the craters
(10) of the maria tend to be much smaller. It is now known that the vast majority of the Moon's
craters were formed by the impact of solid bodies with the lunar surface.
Most of the near side of the Moon was thoroughly mapped and studied from telescopic
pictures years before the age of space exploration. Earth-based telescopes can resolve
objects as small as a few hundred meters on the lunar surface. Close observation of
(15) craters, combined with the way the Moon diffusely reflects sunlight, led to the
understanding that the Moon is covered by a surface layer, or regolith, that overlies the
solid rock of the Moon. Telescopic images permitted the cataloging of a bewildering array
of land forms. Craters were studied for clues to their origin; the large circular maria were
(20) seen. Strange, sinuous features were observed in the maria. Although various land forms
were catalogued, the majority of astronomers' attention was fixed on craters and their
origins.
Astronomers have known for a fairly long time that the shape of craters changes as
they increase in size. Small craters with diameters of less than 10-15 km have relatively
(25) simple shapes. They have rim crests that are elevated above the surrounding terrain,
smooth, bowl-shaped interiors, and depths that are about one-fifth to one-sixth their diameters.
The complexity of shape increases for larger craters.
What does the passage mainly discuss？
A．What astronomers learned from the Surveyor and Apollo space missions
B．Characteristics of the major terrains of the Moon
C．The origin of the Moon's craters
D．Techniques used to catalogue the Moon's land forms
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