如图所示，质量为M的木块静止在光滑水平面上，质量为m的子弹以水_爱下问搜题

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问题选择题

如图所示，质量为M的木块静止在光滑水平面上，质量为m的子弹以水平速度v₀射入木块，并留在木块里．已知在子弹射入木块的过程中子弹发生的位移为s₁，木块发生的位移为s₂，子弹进入木块深度为s，子弹受到阻力大小恒为f，子弹射入木块后二者的共同速度为v_t，不计空气阻力影响，下列说法中不正确的是（　　）

A．fs1=

m

v

20

2

-

mvt2

2

B．fs2=

Mvt2

2

C．fs=

m

v

20

2

-

(m+M)vt2

2

D．fs=

m

v	20
2

-

Mvt2

2

答案

A、以子弹为研究对象，由动能定理得：-fs₁=

1

2

m

v

2t

-

1

2

m

v

20

…①

则得：fs₁=

1

2

m

v

20

-

1

2

m

v

2t

．故A正确．

B、以木块为研究对象，根据动能定理得，子弹对木块做功等于木块动能的增加，即fs₂=

1

2

M

v

2t

…②．故B正确．

C、D因为s=s₁-s₂，由①+②得，-fs=

1

2

（M+m）

v

2t

-

1

2

m

v

20

，则得 fs=

1

2

m

v

20

-

1

2

（M+m）

v

2t

．故C正确，D错误．

本题选错误的，故选：D

填空题

在应用程序生成器的“常规”选项卡中。选择程序类型时选中“正常”，将生成一个在Visual FoxPro主窗口运行的【6】应用程序。

填空题

Tragedies have a way of making people rethink their (1) and find a new focus. They make people think about what a society needs in order to (2) . The notion of doing something to take control of society or of our fate as humans might be dated back to ancient times of the (3) . Now, in the early 21st century, " social (4) " are trying to take back some (5) over society’s direction once again. A social inventor is not necessarily a social (6) , a social (7) or someone who works in a (8) industry or invents new (9) and consumer products. A social inventor is using the power of (10) thinking, to come up with ideas for (11) in certain communities or sections of society. They have a vision of a (12) world and create new systems or practices. Their ideas may seem (13) or impossible. They are usually quite (14) people. But some of these creative thinkers have (15) and quietly changed the way we live. Social inventions do not have to be (16) . Sometimes they are new (17) for neighborhoods or communities, or even very (18) ideas. The idea of social inventions has become so popular in recent years. It shows how much people desire to make a (19) in our society and not remain (20) .

Tragedies have a way of making people rethink their (1) and find a new focus. They make people think about what a society needs in order to (2) . The notion of doing something to take control of society or of our fate as humans might be dated back to ancient times of the (3) . Now, in the early 21st century, " social (4) " are trying to take back some (5) over society’s direction once again. A social inventor is not necessarily a social (6) , a social (7) or someone who works in a (8) industry or invents new (9) and consumer products. A social inventor is using the power of (10) thinking, to come up with ideas for (11) in certain communities or sections of society. They have a vision of a (12) world and create new systems or practices. Their ideas may seem (13) or impossible. They are usually quite (14) people. But some of these creative thinkers have (15) and quietly changed the way we live. Social inventions do not have to be (16) . Sometimes they are new (17) for neighborhoods or communities, or even very (18) ideas. The idea of social inventions has become so popular in recent years. It shows how much people desire to make a (19) in our society and not remain (20) .