问题 计算题

如图所示水平传送带以4m/s的速度匀速运动,传送带两端AB间距为20m,将一质量为2Kg的木块无初速地放在A端,木块与传送带的动摩擦因数为0.2,求木块由A端运动到B端所用的时间。(g=10m/s2

答案

6s

题目分析:对木块受力分析如图

竖直方向物体处于平衡状态,  

所以          

          

设经t速度达到4m/s则

v=at                

   

所以在没有到达B点以前物体速度达到与传送带相同,剩余距离物体与传送带以相同速度匀速运行。

            

木块由A端运动到B端所用的时间      

点评:传送带问题的难点在于判断物体速度和传送带速度之间的关系,以及物体在传送带上加速(减速)的距离和时间。

选择题
阅读理解

E

Computer mouse is no longer so strong. A Canadian engineer has invented a system that enables a computer user to push a cursor(光标)across a screen simply by moving his or her nose .He calls his nose-driven mouse a mouse.

The inventor ,Dmity Gorodnichy ,came up with the idea for the mouse while building computer software that would help astronauts operate the Canadarm—a long robotic arm on the U.S. space shuttle .His system employs a web-camera that recognizes a computer user’s nose from 25 pixels ,or points of light. Dmity chose the nose because its position remains relatively constant no matter which way the head moves .The system keeps track of the pixels, and the user matches the movements of his or her nose with the progress of the cursor across the screen.

The mouse keeps track of the eyes too. Two blinks(眨眼)are a “double click,” which turns the mouse on or off.

The mouse has received mixed comments from those who hold opposite opinions. One called it “a pointless waste of technology” . Another predicted that the nouse will fail to catch on because it makes users “look silly.” Dmity has already adapted the nouse for NousePong, a video game ,and NousePaint ,a drawing program.

He also predicts that the mouse will attract the people who have suffered from specific disease-pain ,senselessness ,or trembling in the hand caused by the frequent repetition of movements of the wrist and fingers ,such as typing at a computer keyboard .His next plan is to adapt the nouse for use by paralyzed(瘫痪)patients in hospitals .With two blinks of the eyes ,patients could double-click for help.

72.The best title for this passage is probably      .

A.Mouse Driven by Nose

B.Cursor Moved Without fingers

C.New Computer System for Astronauts

D.New Type of Mouse for Patients

73.The nouse is a system working by means of          .

A.keeping track of the points of light

B.moving one’s nose or blinking

C.moving cursor across the screen

D.matching the user’s nose with eyes

74.The underlined phrase “catch on” means “       ”.

A.become popular     B.be used      C.get improved        D.be made

75.Dmity predicts that the nouse will be more used to help          .

A.those who have eye trouble

B.develop a video game and drawing program

C.those traveling in space

D.the disabled with the hand and paralyzed patients