问题 问答题

如图所示,在y=0和y=2m之间有沿着x轴方向的匀强电场,MN为电场区域的上边界,在x轴方向范围足够大.电场强度的变化如图所示,取x轴正方向为电场正方向.现有一个带负电的粒子,粒子的

q
m
=1.0×10-2 C/kg,在t=0时刻以速度v0=5×102m/s从O点沿y轴正方向进入电场区域,不计粒子重力作用.求:

(1)粒子通过电场区域的时间;

(2)粒子离开电场的位置坐标;

(3)粒子通过电场区域后沿x方向的速度大小.

答案

(1)因粒子初速度方向垂直匀强电场,

在电场中做类平抛运动,

所以粒子通过电场区域的时间

t=

y
v0
=4×10-3s

(2)粒子在x方向先加速后减速,加速时的加速度

a1=

E1q
m
=4m/s2

减速时的加速度

a2=

E2q
m
=2m/s2                            

x方向上的

s=

1
2
a1(
T
2
)
2
 +a1(
T
2
)
2
-
1
2
a2 (
T
2
)
2
=2×10-5m

因此坐标

(-2×10-5m,2m)                                  

(3)粒子在x方向的速度

vx=a1

T
2
-a2
T
2
=4×10-3m/s

答:(1)粒子通过电场区域的时间为4×10-3s;

(2)粒子离开电场的位置坐标为(-2×10-5m,2m);

(3)粒子通过电场区域后沿x方向的速度大小为4×10-3m/s.

阅读理解

These amazing animals prove that love lives on four legs.

A little girl's lifeline

A pig that calms kids

When Lois Brady, a famous doctor in America, visits special-needs students in San Francisco schools, she often brings along Buttercup, a black pig from Vietnam. The pig is very calm and friendly and has been trained to offer comfort (安慰) to patients as well.

A Lion's big heart

With paws (爪子) the size of dinner plates, bright black eyes and a golden mane (鬃), Jupiter, a 13-year-old 250kg lion, was brought to the rescue (援救) center by Anna. In the past two years, Anna has developed a very close relationship with Jupiter.

小题1:The best title to explain the main idea of the text is “_________”

A. Hero pets                           B Small pets

C. Kids' friends                       D Special visits

小题2:Which of the following do you think is the right match?

A.Alida →a lion

B.Buttercup →a pig

C.Lois →a sick girl

D.Jupiter → a doctor小题3:How long has Mr. Gibbs been with Alida?

A.For about 45 minutes

B.For about 10 months

C.For over 3 years

D.For over 2 years小题4:In which of the following pictures can you find Anna?

A.   B.   C.   .D

小题5:Which of the sentences is Not true according to the passage?

A.Alida has suffered from serious lung disease since she was 10 months old

B.The black pig can calm the kids and offer comfort to them.

C.Mr. Gibbs is a loyal(忠诚的) dog which loves its owner.

D.Anna brought Jupiter to the rescue center for fun.

单项选择题