问题 填空题

用如图所示装置来验证动量守恒定律.质量为mA的钢球A用细线悬挂于O点,质量为mB的钢球B放在离地面高度为H的小支柱N上,O点到A球球心的距离为L,使悬线在A球释放前伸直,且线与竖直线夹角为α,A球释放后摆到最低点时恰与B球正碰,碰撞后,A球把轻质指示针OC推移到与竖直线夹角β处,B球落到地面上,地面上铺有一张盖有复写纸的白纸D,保持α角度不变,多次重复上述实验,白纸上记录到多个B球的落点.(已知当地的重力加速度为g)

(1)为验证两球碰撞过程动量守恒,应测出数值的物理量有S以及______.(用题中字母表示)

(2)用测得的物理量表示碰撞前后A球、B球的动量:PA=______,PA′=______.PB=0,PB′=______.

答案

(1)实验过程中需要求出两小球碰撞前后的动量,因此需要知道小球的质量与速度,小球的速度可以由动能定理与平抛运动知识求得,因此该实验需要测量的物理量有:小球的质量mA、mB,倾角α与β,球B飞出时的高度H,绳长L;即需要测量的量有:mA、mB、α、β、H、L.

(2)小球从A处下摆过程只有重力做功,机械能守恒,由机械能守恒定律得:

mAgL(1-cosα)=

1
2
mAvA2-0,解得:vA=
2gL(1-cosα)
,则PA=mAvA=mA
2gL(1-cosα)

小球A与小球B碰撞后继续运动,在A碰后到达最左端过程中,机械能再次守恒,

由机械能守恒定律得:-mAgL(1-cosβ)=0-

1
2
mAvA2,解得vA′=
2gL(1-cosβ)

PA′=mAvA′=mA

2gL(1-cosβ)

碰撞后B球做平抛运动,水平方向:S=vB′t,竖直方向H=

1
2
gt2

解得vB′=S

g
2H
,则碰后B球的动量PB′=mBvB′=mBS
g
2H

故答案为:(1)mA、mB、α、β、H、L;(2)mA

2gL(1-cosα)
;mA
2gL(1-cosβ)
;mBS
g
2H

完形填空
There was once a lonely girl who wanted love very much. One day      she was walking in the forests, she found two dying birds. She took them home and put them in a small     . She was happy to have two “friends”. She     them with love and the birds grew strong. One day the girl happened to     the door of the cage open. The larger and the     of the two flew out of the cage. The girl was     that it would fly away. She caught it quickly. She felt glad that she caught the bird before it could fly away. Suddenly she couldn’t     a sound from the bird. When she opened her     , the bird was already dead. Her      killed the bird!Then she noticed       bird jumping up and down inside the cage. She could feel       great need for freedom. It wanted to fly into the clear, blue     . So she lifted it from the cage and let it fly away     . The bird circled once, twice, and three times. The girl watched as the bird flew. She didn’t care about      the bird any more. She wanted it to be happy. Suddenly the bird flew closer and landed softly on her shoulder. It sang the     song she had ever heard.
The fastest way to lose love is to hold on it too tightly, and the best way to keep love is to give it wings(翅膀).
小题1:
A.whileB.afterC.beforeD.until
小题2:
A.boxB.basket C.cageD.bag
小题3:
A.looked forB.looked at C.looked afterD.looked over
小题4:
A.forgetB.leaveC.lockD.close
小题5:
A.strongerB.lazierC.weakerD.smaller
小题6:
A.gratefulB.proudC.afraidD.happy
小题7:
A.listenB.makeC.describeD.hear
小题8:
A.doorB.windowC.handD.mouth
小题9:
A.loveB.jokeC.luckD.wish
小题10:
A.one B.the other C.anotherD.other
小题11:
A.itB.itsC.it’sD.it was
小题12:
A.seaB.hill C.forestD.sky
小题13:
A.angrilyB.happilyC.loudlyD.highly
小题14:
A.losingB.loving C.killingD.feeding
小题15:
A.worstB.oldestC.newestD.sweetest
单项选择题