问题 问答题

滑雪是一项既浪漫又刺激的体育运动.在一次滑雪运动中,运动员从山坡上自由滑下,最后停在一水平的运动场地上.这一运动过程可简化为如图所示的物理模型.物体从斜面上的A点由静止开始下滑,经过B点后进入水平面(设经过B点前后速度大小不变),最后停在水平面上.设物体与斜面间以及水平面间的动摩擦因数都为μ,μ=0.2,斜面倾角θ=37°物体经过水平面上的某一点P时的速度vp=30m/s,从A到P滑动时间t=17s,(重力加速度g=10m/s2,sinθ=0.6),求:斜面AB的长度S.

答案

设物体在斜面上滑动时加速度大小为a1、所用时间为t1,在水平面上滑动时加速度大小为a2

则根据牛顿第二定律有:

mgsinθ-μmgcosθ=ma1

得:a1=g(sinθ-μcosθ)

μmg=ma2

得:a2=μg

又:vp=a1t1-a2(t-t1

解得:t1=10s

故斜面的长度为:s=

1
2
a1t12

代入解出:S=220m

答:斜面AB的长度S是220m.

单项选择题
阅读理解

NEW YORK—Microsoft on Monday made another effort to challenge Apple’s iPhone and Google’s Android in the exploding smartphone market—launching a wireless operating system,Windows Phone 7.

Consumers will consider it“always delightful and thoroughly mine,”Microsoft CEO Steve Ballmer said at a launch event. Ballmer said last year that Microsoft had“screwed up”with its Windows Mobile operating system.For example,it failed to keep up with touch-screen innovations that make iPhones and Android phones easy to use.

Microsoft fell from third to fourth place in market share this year,behind BlackBerry,iPhone and Android. Only 10.8% of smartphone owners used Microsoft’s system in August,down from 18% last December.

But Windows Phone 7 is“a total departure from anything they’ve done”.Microsoft says it sought to simplify common activities. For example,you can instantly take a picture with a phone’s camera by pushing a button on the device. You don’t have to first awaken it from its sleep mode and launch the camera application. You also can program the phones to automatically upload photos to Facebook or other social network sites in a couple of seconds. Users can easily work with Microsoft Office contact and calendar information as well as documents created in Microsoft’s Word,Excel and PowerPoint.

The phones will not show videos built on Adobe’s Flash platform,widely used by services including YouTube and Hulu.

AT&T will offer the first Windows Phone 7 smartphone,the Samsung Focus,on Nov.8.Soon after,it will have the LG Quantum and HTC Surround. Each will cost S|  199.99 with a two-year service contract. T-Mobile will have two Windows Phone 7 models out for the holiday shopping season:the HTC HD7 and Dell Venue Pro. It did not say how much they’ll cost.

小题1:What is the main idea of paragraph 4?

A.Why Microsoft fell behind others.

B.How to use Windows Phone7.

C.Advantages of Windows phone7.

D.Speed of Windows phone7.小题2:What does the underlined phrase“screwed up”in the 2nd paragraph probably mean?

A.To make a bad mistake.

B.To make big progress.

C.To achieve main goals.

D.To keep up with others.小题3:Which of the following phones will NOT use Windows Phone 7 operating system?

A.Quantum.

B.Surround.

C.Android.

D.Focus.小题4:Why did Microsoft see a drop in market share last year?

A.Because its operating system didn’t catch up with changes.

B.Because its phones can’t show videos from YouTube.

C.Because it was inconvenient to take photos using its phones.

D.Because its system was based only on Microsoft soft wares.小题5:Which of the following can be the best title of the passage?

A.Smartphone Market Welcomes New Giant

B.Microsoft to Fight Back on Smartphone

C.Mobile Phones Getting Smarter and Easier

D.Microsoft Proved a Failure in Smartphone