问题 计算题

如图所示,甲车的质量是2 kg,静止在光滑水平面上,上表面光滑,右端放一个质量为1 kg的小物体.乙车质量为4 kg,以5 m/s的速度向左运动,与甲车碰撞以后甲车获得8 m/s的速度,物体滑到乙车上.若乙车足够长,上表面与物体的动摩擦因数为0.2,则物体在乙车上表面滑行多长时间相对乙车静止?(g取10 m/s2)

答案

0.4 s

题目分析:乙与甲碰撞动量守恒:mv=mv′+mv

小物体m在乙上滑动至有共同速度v,对小物体与乙车运用动量守恒定律得:

mv′=(m+m)v,

对小物体应用牛顿第二定律得  a=μg

所以   t=

代入数据得   t="0.4" s。

点评:本题考察了相互作用力的物体的动量守恒定律的运用和理解。

阅读理解

A yoga master made a shocking statement that Abraham Lincoln had been a Himalayan yogi in a past life.Lincoln delivered a proclamation setting up Thanksgiving as an American holiday in 1863.Research throws light on a possible Hindu (印度的)origin for the American celebration of Thanksgiving.

"The holiday of Thanksgiving has a Hindu origin," says Richard Salva, author of a book on the reincarnation (转世)of Abraham Lincoln entitled Soul Journey: From Lincoln to Lindbergh which is based on a statement by the great master of yoga, Paramhamsa Yogananda, who declared that Abraham Lincoln had been a Himalayan yogi in a past life, and that he was reborn as the famous pilot, Charles Lindbergh.

“During my search for signs of a past-life yoga practice,” SaIva said, “I noticed that President Lincoln repeatedly chose Thursdays as national days of prayer, fasting (禁食),and thanksgiving.This was interesting, because Thursday is considered a holy day — a day for prayer, fasting, and spiritual reflection — among Hindus, who call it “guru day”.”

“Lincoln also set aside time on Thursdays to grieve(哀悼) for his son,Willie, who died in Washington.Clearly, Thursdays had a spiritual significance in Lincoln's mind.

In his book, Richard Salva presents more than 500 connections between Lincoln, Lindergh, and the ancient spiritual science of yoga. The connections run through every aspect of the human condition and provide convincing evidence that Lincoln had had a Hindu past life.

More than one out of every five Americans today believes in reincarnation—yet few are aware of how past-life patterns affect them. Soul Journey tries to fill this gap, by offering a substitute experience of reincarnation. Through clear and persuasive similarities between the lives of Lincoln and Lindbergh, the book discovers how the hidden laws of fate and reincarnation impact the events of his or her daily life. It addresses other issues, such as the secret spiritual history of America's greatest president, including his past life as a Himalayan yogi; the hidden clues that reveal past lives; the greatness he achieved; and the spiritual principles behind the yoga postures that millions now practice.

小题1:Based on Richard Salva’s view, ______.

A.Hindus started the holiday of Thanksgiving

B.the Americans copied Thanksgiving from Hindus

C.Charles Lindbergh had been a Himalayan yogi

D.Thanksgiving had Hindus roots小题2:We can draw a conclusion from the passage that ______.

A.in India all the prayers are done on Thursday

B.in India Thursday is a religious day

C.Abraham Lincoln was once a famous pilot

D.Paramhamsa Yogananda once taught Lincoln yoga小题3:When it came to the comparison between Lincoln and Lindbergh, the author held a ______ attitude.

A.neutral

B.doubtful

C.negative

D.positive

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