问题 选择题

重为G的苹果从树上竖直下落,若苹果在空中所受阻力小于G,则苹果在竖直下落过程中受到的合力大小(  )

A.等于G

B.等于0

C.大于G

D.小于G

答案

苹果下落时所受重力的方向竖直向下,所受阻力的方向竖直向上,即苹果受到的是同一直线上反方向的两个力;

故苹果的合力大小F=G-f<G,合力方向竖直向下;

故选D.

问答题 简答题
单项选择题

Comparisons were drawn between the development of television in the 20th century and the diffusion of printing in the 15th and 16th centuries. Yet much had happened between. As was discussed before, it was not until the 19th century that the newspaper became the dominant preelectronic mediam, following in the wake of the pamphlet and the book and in the company of the periodical. It was during the same time that the communications revolution speeded up, beginning with transport, the railway, and leading on through the telegraph, the telephone, radio, and motion pictures into the 20th - century world of the motor car and the air plane. Not everyone sees that processin perspective. It is important to do so.

It is generally recognized, however, that the introduction of the computer in the early 20th century, (48) by the invention of the integrated circuit daring the 1960s, radically changed the process, although its impact on the media was not immediately (49) . As time went by, computers became smaller and more powerful, and they became "personal" too, as well as (50) , with display becoming sharper and storage (51) increasing. They were thought of, like people, (52) generations, with the distance between generations much (53) .

It was within the computer age that the term "information society" began to be widely used to describe the (54) within which we now live. The communications revolution has (55) both work and leisure and how we think and feel both about place and time, but there have been (56) view about its economic, political, social and cultural implications. "Benefits" have been weighed (57) "harmful" outcomes. And generalizations have proved difficult.

50()

A.institutional

B.universal

C.fundamental

D.instrumental