问题 问答题

如图所示,质量为m=0.05kg的小球A,用长为L=0.lm的细绳吊起处于静止状态(小球与水平地面接触,但无相互作用),光滑斜面的底端与A相距S=2m.现有一滑块B质量也为m,从固定的斜面上高度h=1.3m处由静止滑下,与A碰撞后粘合在一起.若不计空气阻力,且A和B都可视为质点,B与水平地面之间的动摩擦因数μ=0.25,g取10m/s2.求:

(1)B与A碰撞前瞬间,B速度的大小vB

(2)B与A碰撞后粘合在一起的瞬间,二者共同速度的大小VAB

(3)B与A碰撞后瞬间受到细绳拉力的大小F.

答案

(1)滑块B从斜面高为h处开始下滑到与A碰撞前的过程中,

由动能定理可得:mgh-μmgs=

1
2
mvB2-0,

解得:vB=4m/s;

(2)B与A碰撞过程中,由动量守恒定律得:

mvB=(m+m)vAB,解得:vAB=2m/s;

(3)A与B碰后一起做圆周运动,

由牛顿第二定律得:F-2mg=2m

v2AB
L

解得:F=5N;

答:(1)B与A碰撞前瞬间,B速度的大小为4m/s;

(2)B与A碰撞后粘合在一起的瞬间,二者共同速度的大小为2m/s;

(3)B与A碰撞后瞬间受到细绳拉力的大小为5m/s.

听力题

根据所给首字母或中文意思,用单词的适当形式填空 (每个1分, 共20分.)

小题1:He was c__________(好奇的) to know what was going on in the neighborhood.

小题2:The law applies to all EU countries; Britain is no e__________ (例外).

小题3:It was pouring. The hunter got inside a hollow tree for s__________ (庇护).

小题4: This new pay-TV channel sends s__________ (信号) via satellite to cable companies.

小题5:They o__________(提供) him a very good job, but he turned it down.

小题6:The entire s__________ (员工) has done an outstanding job this year.

小题7:A good diet is e__________ (必不可少的) for everyone.

小题8:His dog became his closest c__________(同伴).

小题9:She a__________ (申请) for a job with the local newspaper yesterday.

小题10:She keeps a bottle of gin h__________ (隐藏的) behind a stack of books.

小题11:I want to do research on Mark Twain. Is there a b__________ (传记) about him?

小题12: He had a v__________(生动的) picture of her in his mind.

小题13: Sorry to d_________ (打扰) you, but I have an urgent message.

小题14:He finally won his f__________(自由) after twenty years in jail.

小题15:Our o__________(起初的) plan was to go camping, but it was pouring with rain.

小题16:Many endangered species now face e__________ (灭绝)

小题17:This kind of apples is more expensive because they are i__________(进口)from abroad.

小题18:The hotel is not modern, but it does have the a__________ (优势) of being close to the city.

小题19:Jordan, a talented leader, led his team to v__________(胜利) .

小题20:She s_________ (得分) an average of 95 in the last test.

问答题 简答题