假设地球可视为质量均匀分布的球体,已知地球表面重力加速度在两极的大小为,在赤道的大小为g;地球自转的周期为T,引力常量为G,求:(1)地球的密度;(2)若地球自转角速度逐渐增大,使赤道上物体恰好“飘”起时地球的自转周期。 答案:【答案】(1);(2)【解析】(1)质量为m的物体,在两极:①在赤道上:②地球密度:③解①、②、③式得④(2)当地球自转周期为时,赤道上物体恰好“飘”起⑤由①②⑤得
第三部分: 完形填空(共20小题;每小题2分,满分40分)
阅读下面短文,从短文后各题所给的四个选项(A、B、C和D)中,选出空白处的最佳选项,并在答题卡上将该项涂黑。
The back door of the ambulance was suddenly
shut and the driver ran to the front, jumped into the seat, and started the
engine。 Inside were
the 26 parents, Mr。 and Mrs。 Green。
The mother was holding their baby daughter, Ally。 The girl had some 27
stuck in her throat and could 28 breathe。
The driver, Mr。 White, turned on his siren(警报器) and sped towards the
29 hospital, fighting against the time。 The 30
ahead of him pulled out of the way 31 he drove through
the busy traffic。 From
the back of the 32 the parents were shouting at him to
be __33 , since Ally had
almost stopped 34 。 In front of him he saw some traffic 35 , with the
red “Stop” light shining。 Mr。
white knew he had no time to 36 , so he drove straight
through the traffic lights。
Coming towards him from his right was a
taxi with the 37 closed, and the driver was playing his
radio, He did not 38 the ambulance。 The lights were
green; 39 he drove straight on into the ambulance。
Mr。 White tried to stop his ambulance, but it was too
40 。 It hit
the taxi。 Everyone
was shaken, but no one was hurt。 Mr。
White looked to see 41 little Ally was。 He was astonished to see
relief(宽慰) instead
of 42 on the faces of the parents。
“Look!” cried Mrs。 Green。 “She is breathing again。”
“It 43 have been
the crash,” said her husband, “It 44 the food out of
her throat。”
The baby’s color was turning
45 , and she was crying in a loud but healthy voice。 They were all joyful, and
quite forgot about the accident。
26。 A。
worried
B。
angry C。
satisfied
D。 surprised
27。 A。
honey
B。
drinks C。
food
D。 water
28。 A。
never
B。
almost C。 hardly
D。 simply
29。 A。
modern
B。
promising C。 children’s D。 nearest
30。 A。
interviewers B。 drivers
C。
cars
D。 parents
31。 A。
that
B。
as
C。 if
D。 as though
32。 A。
street
B。
cars
C。
traffic
D。 ambulance
33。 A。
quick
B。
convenient C。
anxious
D。 calm
34。 A。
breathing
B。
circulating C。
saying
D。 talking
35。 A。
signs
B。
policemen C。
lights
D。 marks
36。 A。
stop
B。
spare C。
lose
D。 miss
37。 A。 engine B。
car
C。
door
D。 window
38。 A。hear
B。
see
C。
find
D。 notice
39。 A。
however
B。
so
C。
but D。 on the other hand
40。 A。
dangerous
B。
late
C。
careless
D。 quick
41。 A。
how
B。
what
C
where
D。 who
42。 A。
pleasure
B。
anger C。 fear
D。 surprise
43。 A。
may
B。 can
C。
should
D。 must
44。 A。
took
B。
picked C。
knocked
D。 pulled
45。 A。
common
B。
normal C。
general
D。 ordinary