问题 填空题

请完成以下小题.

(1)如图1所示,是某研究性学习小组做“探究橡皮筋做的功和物体速度变化的关系”的实验,图中是小车在一条橡皮筋作用下弹出,沿木板滑行的情形,这时,橡皮筋对小车做的功记为W.当我们用2条、3条…完全相同的橡皮筋并在一起进行第2次、第3次…实验时,每次橡皮筋都拉伸到同一位置释放,小车每次实验中获得的速度由打点计时器所打的纸带测出.

①除了图1中的已给出的实验器材外,还需要的器材有______;

②实验时为了使小车只在橡皮筋作用下运动,应采取的措施是______;

③在用图示装置做“探究动能定理”的实验时,下列对于实验步骤的描述中,正确的是______

A.通过改变橡皮筋的条数改变拉力做功的数值

B.通过改变橡皮筋的长度改变拉力做功的数值

C.通过打点计时器打下的纸带来测定小车加速过程中获得的最大速度

D.通过打点计时器打下的纸带来测定小车加速过程中获得的平均速度

(2)在做“研究匀变速直线运动”的实验时,某同学得到一条用电火花计时器打下的纸带如图甲所示,并在其上取A、B、C、D、E、F、G7个计数点,每相邻两个计数点之间还有4个点图中没有画出,电火花计时器接50Hz交流电源.他经过测量并计算得到电火花计时器在打B、C、D、E、F各点时纸带运动的瞬时速度如下表:

对应点BCDEF
速度(m/s)0.1410.1800.2180.2620.301
①设电火花计时器打点的时间隔为T,则计算vF的公式为vF=______(用题中所给物理量符号表示)

②根据上表中的数据,以A点对应的时刻为计时的开始,即t=0.试在图乙所示坐标系中合理地选择标度,作出v-t图象,并利用该图象求物体的加速度a=______m/s2

答案

(1)①该实验用到打点计时器,所以需要交流电源,要测量长度,还需要刻度尺;

②小车下滑时受到重力、细线的拉力、支持力和摩擦力,要使拉力等于合力,则应该用重力的下滑分量来平衡摩擦力,故可以将长木板的一段垫高平衡小车所受的摩擦力.

③A:橡皮筋拉小车时的作用力是变力,我们不能求变力做功问题,但选用相同的橡皮筋,且伸长量都一样时,橡皮条数的关系就是做功多少的关系,因此,可以不需求出变力功的大小,就知道功的关系.所以A正确,B错误;

 C、D:当橡皮筋做功完毕小车应获得最大速度,由于平衡了摩擦力所以小车以后要做匀速运动,相邻两点间的距离基本相同.所以计算小车速度应该选择相邻距离基本相同的若干个点作为小车的匀速运动阶段,用这些点计算小车的速度.故C对D错误.

综上可知A、C正确.

故选AC

(2)根据匀变速直线运动中时间中点的瞬时速度等于该过程中的平均速度,电火花计时器的周期为T,所以从E点到G点时间为10T,有:

vF=

xEG
10T
=
d6-d4
10T

根据图中数据,利用描点法做出图象如下;

图象斜率大小等于加速度大小,故a=

△v
△t
=0.40m/s

故答案为:(1)交流电源、刻度尺;将长木板的一段垫高平衡小车所受的摩擦力;AC;(2)

d6-d4
10T
;0.40.

阅读理解

阅读理解。

    A "lost tribe" that reached America from Australia may have been the first Native

Americans, according to a new theory.

    If proved by DNA evidence, the theory will break long established beliefs about the

southerly migration of people who entered America across the Bering Strait, found it

empty and occupied it.

    On this theory rests the belief of Native Americans to have been the first true

Americans. They would be classified to the ranks of escapee, beaten to the New World by

Aboriginals (土著人) in boats.

    To a European, this may seem like an academic argument, but to Americans it is a

philosophical question about identity, Silvia Gonzales, of Liverpool University said.

    Her claims are based on skeletons found in the California Peninsula of Mexico that

have skulls quite unlike the broad Mongolian features of Native Americans. These narrow-

skulled people have more in common with southern Asians, Aboriginal Australians and people

of the South Pacific Region.

    The bones, stored at the National Museum of Anthropology (人类学) in Mexico City,

have been carbon-dated and one is 12,700 years old, which places it several thousand

years before the arrival of people from the North. "We think there were several migration

waves into the Americas at different times by different human groups," Dr. Gonzales said.

"The timing, route and point of origin of the first colonization of the Americas remains

a most contentious topic in human evolution."

    But comparisons based on skull shape are not considered conclusive by anthropologists,

so a team of Mexican and British scientists, backed by the Natural Environment Research

Council, has also attempted to take out DNA from the bones. Dr. Gonzales declined yesterday

to say exactly what the results were, as they need to be checked, but indicated that they

were consistent (一致) with an Australian origin.

1. It is generally considered that the first Native Americans came from ______. [ ]

A. North Asia

B. Australia

C. South Pacific

D. South Asia

2. The skeletons found in the California Peninsula of Mexico have ______. [ ]

A. the broad skull shape

B. the narrow skull shape

C. different features of Aboriginal Australians

D. the same features of Native Americans

3. The underlined "contentious" is similar in meaning to "______". [ ]

A. likely to cause great interest

B. difficult to solve

C. well-known to all

D. likely to cause argument

4. Which of the following statements is true according to the text? [ ]

A. Research on skulls can draw an exact conclusion.

B. DNA tests have proved the fact that the first Native Americans came from Australian.

C. Scientists are still not sure about the origin of the Native Americans.

D. People began to enter America across the Bering Strait about 12,700 years ago.

多项选择题