质量为2kg的平板车Q上表面水平，原来静止在光滑水平面上，平板车_爱下问搜题

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问题问答题

质量为2kg的平板车Q上表面水平，原来静止在光滑水平面上，平板车左端静止着一块质量为2kg的物体P，一颗质量为0.01kg的子弹以700m/s的速度水平瞬间射穿P后，速度变为100m/s，若P、Q之间的动摩擦因数为0.5，则：

（1）子弹打穿P后，物体P的速度多大？

（2）若最终P没有从小车上掉下来，小车至少多长？

答案

（1）以子弹与P组成的系统为研究对象，以子弹的初速度方向为正方向，由动量守恒定律得：

m₁v₁=m_pv_p+m₁v₂，

代入数据得：v_p=3m/s；

（2）以P、Q组成的系统为研究对象，系统动量守恒，以P的初速度方向为正方向，由动量守恒定律得：

m_pv_p=（m_p+m_Q）v，

代入数据得：v=1.5m/s，

由能量守恒定律得：

1

2

m_pv_p²=

1

2

（m_p+m_Q）v²+μm_pgL，

解得：L=0.45m；

答：（1）子弹打穿P后，物体P的速度为3m/s；

（2）若最终P没有从小车上掉下来，小车至少0.45m．

完形填空

Once in Japan there lived two frogs, one of whom made his home near the town of Osaka, while the other lived in Kyoto. 36 , they didn’t know each other. Bothof them liked to see a little of the world: the Kyoto frog wanted to visit Osaka, and the Osaka frog wished to go to Kyoto.
So one morning they 37. However, the journey was more 38 than they had expected, for they didn’t know much about traveling. Half-way between the two towns, at the top of a mountain, the two frogs 39 each other! Soon they fell into 40 .
“What a(n) 41 we are too small, ” said the Osaka frog. “Otherwise, we could see both towns from here, and 42 if it is worth our going on.”
“Oh, that is easily 43 ,” replied the Kyoto frog. “We have only got to stand up on our hind (后面的) legs, and hold on to each other 44 we won’t fall down, and then we can both look at the towns we are 45 to.”
This idea 46 the Osaka frog; he stood up and put his front paws on the 47 of the other frog, who had risen also. There they both stood, stretching themselves as 48 as they could. The Kyoto frog turned his nose towards Osaka, and the Osaka frog, towards Kyoto, but the 49 frogs forgot that when they stood up, their eyes were in the backs of their heads, and that 50 their noses pointed to their destinations, yet their eyes looked at the places 51 which they had come.
“Dear me!” cried the Osaka frog. “Kyoto is 52 like Osaka. It is certainly not worth such a long journey.”
“If I had known that Osaka was only a 53 of Kyoto I should never have traveled all this way,” 54 the frog from Kyoto. Then they started off for their 55 again.

A．Surprisingly

C．Fortunately

D．Undoubtedly

C．turned away

C．encountered

D．embarrassed

A．conversation

B．disagreement

C．competition

D．consideration

C．shortcoming

D．coincidence

A．adventurous

A．destinations

问答题简答题

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