问题 计算题

交管部门强行推出了“电子眼”,机动车违规现象大幅度减少。现有甲、乙两汽车正沿同一平直马路同向匀速行驶,甲车在前,乙车在后,它们行驶的速度均为10m/s。当两车快要到十字路口时,甲车司机看到绿灯已转换成了黄灯,于是紧急刹车(反应时间忽略不计),乙车司机为了避免与甲车相撞也紧急刹车,但乙车司机反应较慢(反应时间为0.5a)。已知甲车、乙车紧急刹车时所受的阻力均为车重的0.4倍,求:

(1)若甲司机看到黄灯时车头距警戒线15m,他采取上述措施能否避免闯红灯?

(2)为保证两车在紧急刹车过程中不相撞,甲、乙两车行驶过程中应保持多大距离?

答案

解:(1)根据牛顿第二定律可得甲车紧急刹车的加速度为

甲车停下来所需时间

这段时间滑行距离

,甲车司机能避免闯红灯

(2)设甲、乙两车行驶过程中至少应保持距离s0,在乙车刹车t2时间两车恰好相遇,则有:

乙车紧急刹车的加速度为

恰好相遇条件:

解得:

阅读理解

2011 TEEN TRIP TO THE LELAND HIGH SNOW PLAY

For Teens Currently in 6th to 12th Grades

LELAND HIGH SNOW PLAY -- Class # 8389

Saturday, February 12, 2011

8:00 a.m. to 7:00 p.m.

Meet at THE UNDERGROUND (Veteran's Building -- 2203 Central Avenue)

Cost per person: $50 ($60 after January 22, 2011) Includes Lunch, Admission and Transportation

With a 4,000 sq. Ft. day-use lodge, the Leland High Snow Play has a huge supply of tubes to choose from, along with awesome tows (拖车) that will tow you up to the top of the hill! Our varied terrains (地形) have something for everyone, while the lodge provides a snack bar, video games, pool tables, five indoor rest rooms, a warm fire, and a sun deck with plenty of tables and chairs overlooking the play area outside. ADDITIONAL LIABILITY FORM REQUIRED FOR THIS TRIP.

Be sure to bring warm clothing and prepare for the cold, but dress in layers in case it warms up. Wear dry boots, socks, and sunscreen. If possible, bring a mobile phone in case of emergency, as well as money for snacks and a light dinner: or bring your own food and drinks.

Meet at The Underground (Veteran's Building -- 2203 Central Avenue) -- don't be late!

Do not bring electronic or fragile items during the trip. The ARPD is not responsible for your personal belongings or money. REFUNDS ARE ISSUED ONLY IF THE ARPD CANCELS THIS TRIP DUE TO WEATHER CONDITIONS.

Click here to download "2011 Leland High Snow Play" flyers and the registration form (PDF, 261KB)

Click here to download "Leland High Snow Play Liability Form" (PDF, 14KB)

1. You may register in person, or mail the completed form to Leland High Snow Play, Inc.

Send the liability form and payment to the ARPD Office, 2226 Santa Clara Avenue, Alameda, 94501.

2. Faxed registration and liability forms accepted with MasterCard/VISA, (510) 747--7566.

3. Online registrations available at www.arpdeplay.com. Make sure you bring your completed liability form on the trip.

小题1:The purpose of the text is to ________.

A.explain the details of a school activity

B.introduce a famous tour agency

C.urge teenagers to climb a snowy mountain

D.advertise a trip to the Leland High Snow Play小题2:People who want to take part in the activity need to ________.

A.pay for dinner themselves

B.climb the hill themselves

C.wear hats to protect themselves from the sun

D.pay for tows individually小题3:From the text we can infer that ________.

A.the weather at the hill is changeable

B.the activity is very dangerous

C.12-year-old children are not allowed on the trip

D.the trip will involve outdoor activities only.小题4:To save money people should ________.

A.climb the hills instead of taking tows

B.bring extra clothing

C.register for the activity before January 22

D.register on the Internet after January 22

单项选择题