搜题请搜索小程序“爱下问搜题”
问题 选择题

一个物体做自由落体运动，那么在任意一秒内（  ）

A．物体的末速度一定比初速度大9.8m/s

B．物体的末速度一定等于初速度的9倍.

C．物体的位移一定等于前一秒内位移的9.8倍

D．物体的位移一定比前一秒内的位移大9.8m

答案

AD

自由落体运动是初速度为0，加速度为g的匀加速直线运动，在运动的过程中，加速度保持不变，速度均匀增大

根据自由落体运动的规律：，在任意一秒内物体的末速度一定比初速度大9.8m/s，A正确；B错误

，所以在任意一秒内物体的位移一定等于前一秒内位移大，所以C错，D对；故答案选AD .

解决本题的关键知道自由落体运动是初速度为0，加速度为g的匀加速直线运动

单项选择题

As one works with color in a practical, or experimental way, one is impressed by two apparently unrelated facts. Color as seen is a mobile, changeable thing (1) to a large extent on the relationship of the color (2) other colors (3) simultaneously. It is not (4) in its relation to the direct stimulus which (5) it. On the other hand, the properties of surfaces that give (6) to color do not seem to change greatly under a wide variety of illumination color, usually (but not always) looking much the same in artificial light as in daylight. Both of these effects seem to be (7) in large part to the mechanism of color (8) .

When the eye is (9) to a colored area, there is an immediate readjustment of the (10) of the eye to color in and around the area (11) . This readjustment does not promptly affect the color seen but usually does affect the next area to which the (12) is shifted. The longer the time of viewing, the higher the (13) , and the larger the area, the greater the effect will be (14) its persistence in the (15) viewing situation. As indicated by the work of Wright and Schouten, it appears that, at (16) for a first approximation, full adaptation takes place over (17) time if the adapting source is moderately bright and the eye has been in (18) darkness just previously. Also, (19) of the persistence of the effect if the eye is shifted around from one object to another, all of which are at similar brightness or have similar colors, the adaptation will tend to become (20) over the whole eye.

11（）

A.noticed

B.alarmed

C.neglected

D.tolerated
查看答案
单项选择题

We have received your letter of 23 November ______ reply to ours of 12 November.

A．to
B．in
C．for
D．on
查看答案