Li Hu第二节(满分25分)Green realized it was an emergency. Mary might faint at any time. If she couldnt receivetimely help, she would suffer severe brain damage, or even die, which would definitely scare hertwo grandchildren. Concerned that she was in such a critical situation where every minute countedfor her life, he immediately called the hospital to find her an ambulance. After being informed ofwhat was going on, two teachers dropped everything without delay, climbed into Greens car andset off. (75 words)When Green and the other two teachers reached the family's home less than ten minutes later,seeing what was happening, they sighed in relief. Everything was well in order. The doctors weregiving first aid to Mary, pressing on her chest. The two kids looked visibly shaken, close to tearsBeside them stood Julia, holding them in her arms and comforting them. Fortunately enough, thequick response from Julia and Green saved Marys life. When she came to herself, she was lifted tothe ambulance and rushed to the hospital. Everybodys face brightened up as the ambulance fadedaway. (75 words

2分(2)M(2分)(3)m1分【解析】(1)由平抛运动规律得竖直方向h=g2,水平方向x=t,解得水平速度w=x°(2)由于水平位移相同,碰后速度越大,则飞行时间越短,竖直方向下落的高度越小,故碰后B球的平均落点应在M处。(3)根据(1)中所求可得,碰前A球的速度vA碰后A、B两球的速度分别为根据动量守恒定律得=mv"+m,化简可得mM=mv×2 A即只要上式成立,则可以验证动量守恒定律

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