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问题 问答题

将石头从19.6m的高处以10m/s的速度水平抛出，抛出后经过1s，另一块石头由同一高度被竖直向下抛出，要使这块石头与第一块同时落地，抛出第二块石头的初速度应为多大？

答案

14.7

单项选择题

吸毒者的平均寿命较一般人群短（）。

A、3－5年

B、5－10年

C、10－15年

D、10－20年
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单项选择题

An analog signal’s characteristic quantity representing data may 66) . at any instant, any value within a continuous (67) . For example, an analog signal may follow continuously the values of another physical quantity representing data.

A discrete signal is composed of (68) elements in time, each element having one or more characteristic quantities which can represent data. Examples of characteristic quantities are amplitude, waveform, (69) , and position in time. A digital signal is a special case of discrete signals, in which data are represented by a (70) number of well-defined discrete values that one of its characteristic quantities may take in time.

（70）处填（）。

A．limited

B．finite

C．restricted

D．bounded
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