问题 填空题

两块厚度相同的木块A和B,紧靠着放在光滑的水平面上,其质量分别为mA=0.5kg,mB=0.3kg,它们的下底面光滑,上表面粗糙;另有一质量mC=0.1kg的滑块C(可视为质点),以vC=25m/s的速度恰好水平地滑到A的上表面,如图所示,由于摩擦,滑块最后停在木块B上,B和C的共同速度为3.0m/s,则木块A的最终速度vA=____________m/s,滑块C离开A时的速度vC′=____________m/s。

答案

2.6,4.2

问答题

American and Japanese researchers are developing a smart car that will help drivers avoid accidents by predicting when they are about to make a dangerous move.

The smart car of the future will be able to tell if drivers are going to turn, change lanes, speed up, slow down or pass another car.

If the driver’s intended action could lead to an accident,the car will activate a warning system or override the move.

(46) " BY shifting the emphasis of car safety away from design of the vehicle itself and looking more toward the driver’s behavior, the developers believe that they can start to build cars that adapt to suit people’s needs , " New Scientist magazine said.

Alex Pentland of the Massachusetts Institute of Technology collaborated on the project with Andrew Liu who works for the Japanese carmaker Nissan.

(47)Tests of their smart car using a driving simulator have shown that it is 95 percent accurate in predicting a driver’s 12 seconds in advance.

(48)The system is based on driving behavior which the researchers say can be divided into chains of sub-actions which include preparatory moves.

It monitors the driver’s behavior patterns to predict the next move.

" To make its predictions, Nissan’s smart car uses a computer and sensors on the steering wheel, accelerator and brake to monitor a person’s driving patterns. (49)A brief training session, in which the driver is asked to perform certain maneuvers, allows the system to calculate the probability of particular actions occurring in two-second time segments, " the magazine said.

Liu has also done work on tracking eye movement to predict driving behavior. (50)He said the smart car could be adapted to monitor eye movement which could give even earlier predictions of when a driver is about to make a wrong move.

(48)The system is based on driving behavior which the researchers say can be divided into chains of sub-actions which include preparatory moves.

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