问题 问答题

在距沙坑表面高h=8m处,以v0=22m/s的初速度竖直向上抛出一质量m=0.5kg的物体,物体落到沙坑并陷入沙坑d=0.3m深处停下.若物体在空中运动时的平均阻力是重力的0.1倍(g=10m/s2).求:

(1)物体上升到最高点时离开沙坑表面的高度H;

(2)物体在沙坑中受到的平均阻力F是多少?

答案

(1)物体上升到最高点时离抛出点h,从抛出到上升到最高点的过程,由动能定理得:

-(mg+f)h=0-

1
2
m
v20

由题意知,f=0.1mg②

由①、②并代入数据得:h=

1
2
m
v20
mg+f
=
1
2
×0.5×222
1.1×0.5×10
m=22m

则离开沙坑的高度 H=8+h=8+22=30(m);

(2)物体在沙坑中受到的平均阻力为F,从最高点到最低点的全过程中:

mg(H+d)-fH-Fd=0

代入数据得:F=

mg(H+d)-fH
d
=
0.5×10×[(30+0.3)-0.1×30]
0.3
N=455N;

答:

(1)物体上升到最高点时离开沙坑表面的高度H为30m;

(2)物体在沙坑中受到的平均阻力F是455N.

单项选择题 A1/A2型题
阅读理解

阅读理解。

     She was known to millions as the "Queen of Crime" or the " Duchess (女公爵) of death". But surprisingly,

she hated violence and blood, and knew nothing of the weapons most often used in murder."I don't think I dare

look at a really horrible and damaged body." Agatha Christie once said.

     But her pen dared travel where her eyes would not. In a 50-year writing career, Christie's murder stories

made her the world's best-known mystery writer. She is outsold only by the Bible and Shakespeare.

     Her works have been turned into films and TV series, and a line of computer games is to be released over

the next six years.

     "My grandmother liked to use new ways to reach people who wanted to enjoy her work," said Christie's

grandson, Mathew Pri- chard."Turning her stories into PC games allows us to introduce classic mysteries to

new audiences.

     Born in 1890 in England, Christie was educated at home and began her writing career while working as a

nurse during World War I. She went on to produce 79 novels and numerous short sto- ries, dying at the age

of 86.

     "With her knowledge of murder, Christie could have been a teacher at police academies," said one fan.

1. By which means can't we learn the works of Christie?

A. Watching TV.

B. Going to the cinema.

C. Reading novels.

D. Playing computer games.

2. Mathew Prichard's words suggest that ____.

A. Christie had been trying to write different stories in different styles

B. Christie was fond of changing styles while writing

C. Christie's works are short of audiences

D. People began to lose interest in Christie's works

3. The fifth paragraph mainly _____ .

A. tells us Christie is a productive writer

B. gives us a brief introduction of Christie

C. tells us when Christie took up writing

D. tells us why Christie was popular