问题 问答题

李老师的家离学校大约10km,为了便于上下班,他购买了一部轻便摩托车来代步,使用的燃料为93#汽油.根据表提供的数据,请回答:

(1)如果李老师上班时骑车的平均速度为36km/h,试根据表中所提供的有关信息,为李老师计算一下,他骑车从家到学校至少需花多少油费?

轻便摩托车93#汽油
燃料汽油密度0.7×103kg/m3
油箱容量7L热值4.5×107J/kg
功率6kW价格4.90元/L
(2)小洪同学学过物理以后,给李老师建议:在上述条件不变的情况下,采用加快车速缩短时间的办法,就一定可以省油费.请你根据自己掌握的知识,分析说明这种方法是否可行.

答案

(1)因为李老师的骑车速度为v=36km/h=10m/s

∵v=

s
t

∴李老师上学校所用的时间t=

s
v
=
10000m
10m/s
=1000s,

摩托车所做的功应为W=Pt=6×103W×1000s=6×106J,

∵所用的汽油放出的热量应为Q=W=6×106J,Q=mq,

∴所以上学校时须用的汽油的质量为:m=

Q
q
=
6×106J
4.5×107J/kg
≈0.133kg,

∵ρ=

m
V

∴所用汽油的体积V=

m
ρ
=
0.133kg
0.7×103kg/m3
=0.19×10-3m3=0.19L,

所以,李老师上学校应花去油费4.90元/L×0.19L=0.93元;

(2)单独从t=

s
v
和W=pt来考虑,在功率P不变的情况下,提高车速可以减小发动机所做功,好象可以省油.但根据W=Fs和P=
W
t
可得,P=Fv,也就是说,在行驶阻力不变的情况下,提高车速v,必然导致发动机的功率P增大,发动机所做的功W增大,进而导致汽油量增大,所以单纯靠提高车速并不一定能减小发动机所做的功、达到省油的目的.故该种方法不可行.

答:(1)他骑车从家到学校至少需花0.93元的油费.

(2)不可行,如上所述.

阅读理解

We arrived at the hospital only to find Dad weak, but his smile was as sure as ever. My husband and I had to work, so our relatives would help him get home from the hospital and look after him. But I wanted Dad to know that we cared about him, too, even when we weren’t with him.

Then I remembered a family tradition (传统) when our children were small. When leaving their grandparents’ home, each child would write a love note for their grandparents to find after we were gone. They hid notes in the food box, or even in the fridge. For days their grandparents would smile as they discovered these notes of the children’s love.

So as I cleaned Dad’s room downstairs before he got home, I began writing notes. Some showed my love. Most notes were in his room downstairs where he would be able to find, but one note was hidden upstairs under his pillow. “Dad, if you have found this note, you must be feeling better. We are so glad!”

My notes were a reminder (提醒的事物) of our love for Dad. Just like his medicines made him better physically (身体上), these would improve his mental (精神的) health. Several weeks later, I made a phone call to Dad and asked what he was doing. He said, “I’ll tell you what I’m doing. I am just reading the note you left under my pillow upstairs!”

64. Which of the following did the author NOT do for her father?

A. Writing notes.            B. Driving her father home. 

C. Making phone calls.       D. Helping to clean her father’s room.

65.  The underlined word “these” (in Paragraph 4) refers to “______”.

A. medicines             B. the relatives’ care and help

C. notes                    D. delicious foods

66. The author hid most notes _____.

A. in Dad’s room downstairs     B. in the food box

C. in the fridge               D. under Dad’s pillow upstairs

67. From the passage we can know the author’s notes couldn’t ______.

A. show her love for Dad            B. make Dad remember something

C. make Dad healthier mentally        D. improve Dad’s physical health

单项选择题