问题 选择题

如图所示,一小钢球从光滑固定斜面的A点静止释放,相继经过B、C两点,AB=BC,则下列分析正确的是(忽略空气阻力的影响)

A.小钢球下滑过程中做匀速直线运动

B.小钢球在AB、BC两段内运动的平均速度相等

C.小钢球所受重力在AB、BC两段内做功相等

D.就A、B、C三点而言,小钢球在A点具有的机械能最大

答案

答案:C

题目分析:小钢球从A处由静止滚下,高度减小,重力势能减小,速度增大(速度越来越大),动能增大,故A、B选项错误;

又因为斜面光滑,所以整个过程能量守恒,则AB、BC两段的高度相等,因此减少的重力势能相等,故小钢球在AB、BC两段内做功相等;而整个过程中小钢球具有的机械能不变,故C选项正确,D选项错误;

故选C.

点评:在做能量的转化这种题时,我们首先要注意能量是否守恒,然后分析哪种能量增加了,哪种能量减少,即为减少的这种能量转化为增加的那种能量.

阅读理解

I do not need a calendar to tell me when it is winter. All I need is my nose. When I wake up in the morning and smell the tasty treats my mom is cooking downstairs, I know winter has arrived.

The first one is the smell of chocolate. During the holiday season (from Thanksgiving to New Year’s Day) my mother makes her special hot chocolate. She always adds a peppermint candy cane (薄荷味拐棍糖) to the drink and tops it with cream.

The hot chocolate gets me out of bed, but it is my mother’s chocolate fudge (软糕) that makes me run downstairs. It is a thick chunk (块) of chocolate that tastes like heaven. My mother adds nuts. That gives it more texture (质感).

But my mother isn’t done yet. She also makes a treat she calls “window panes (窗玻璃)”. She takes a few different colored marshmallows (棉花糖) and melts them together with chocolate. The final product looks like a colorful church window, so we call it “window panes”.

These tasty holiday treats are usually eaten after a meal as a dessert. But don’t tell Santa Claus because I secretly eat them all day long.

小题1:What wakes “me” up in the morning?

A.The alarm clock.

B.My mom.

C.The noise upstairs.

D.The smell of food.小题2: In the author’s eyes, the taste of the chocolate fudge is ____.

A.terrible

B.wonderful

C.awful

D.so so小题3:With nuts, the chocolate fudge tastes _____.

A.softer

B.sweeter

C.harder

D.hotter小题4:The “window panes” the author mentions refer to _____.

A.special hot chocolate drink

B.decorations on the window

C.chocolate cake with fruits on it

D.a mixture of marshmallows and chocolate小题5:Why does the author look forward to the winter?

A.There is plenty of time to play around.

B.The food his mom cooks is mouthwatering.

C.It’s great fun to play outdoors.

D.He can have a good rest during the winter.

多项选择题