问题 解答题

现有一批货物用轮船从甲地运往乙地距离为500海里,已知该船最大速度为45海里/小时,每小时运输成本由燃料费用和其他费用组成。轮船每小时的燃料费用与轮船速度的平方成正比,其余费用为每小时960元。已知轮船速度为20海里/小时,全程运输成本为30000元。

(1)把全程运输成本y(元)表示为速度x (海里/小时)的函数;

(2)为了使全程运输成本最小,轮船应为多大速度行驶?

答案

解:(1)由题意得,每小时燃料费用为,全程所用时间为小时,

则全程运输成本

当x=20时,y=30000,得k=0.6,

故所求的函数为

(2)

当且仅当,即x=40时取等号,

故当轮船速度为40海里/小时时,所需成本最小。

阅读理解

At the age of sixteen, I went on my first volunteer program in West Virginia to repair or build homes for poor families. When we arrived, we discovered that the family we were going to help was living in a trailer(拖车式活动房)that was in poor condition, no bigger than two parking spaces. A group of people had been working on it for two weeks, but every time they finished one problem, another appeared.

We soon decided that the only way was to build a new house. It was something unusual because normally our goal was to repair old homes. The family was pleased with their new house that was 20 by 30 feet with three bedrooms, a bath and a kitchen.

On Tuesday of that week, I asked the family’s three boys, Josh, Eric and Ryan, “What do you want for your new room?” Kids in the families we had helped usually wanted toys or posters, so we were surprised when Josh, the oldest boy said, “We just want beds.” The boys had never slept in a bed. That night we had a meeting and decided that beds would be the perfect gift. On Thursday night, a few adults in our group drove to the nearest city and bought beds and new bedding.

On Friday when we saw the truck coming, we told the family about the surprise. They were very excited.

That afternoon, while we were setting up the beds, Eric ran into the house to watch us with wide eyes. As Maggie, a member of our group, put one of the pillows on the bed, Eric asked, “What is that?”

“A pillow,” she replied.

“What do you do with it?” Eric went on asking.

“When you go to sleep, you put your head on it,” Maggie answered softly. Tears came to our eyes as she handed Eric the pillow.

“Oh . . . that’s soft,” he said, holding it tightly.

Now, when my sister or I start to ask for something that seems very urgent(急迫的), my dad always asks, “Do you have a pillow?” We know exactly what he means.

小题1:Why did the writer’s group build a new house for the family?

A.Because it was their normal work.

B.Because the family asked them to do it.

C.Because the trailer could no longer be repaired.

D.Because they thought it was a perfect gift for the family.小题2:What can we learn from the story?

A.The family needed two parking spaces.

B.The boys of the family wanted toys and posters.

C.The family were excited about the beds and bedding.

D.The writer’s group made some furniture for the family.小题3:What is the best title for this passage?

A.The Pillow

B.A New House

C.The Family

D.An Interesting Program

单项选择题 A1型题