问题
计算题
在排球比赛中，扣球手抓住一次机会打了一个“探头球”，已知来球速度为10 m/s，击回的球速度大小为20 m/s，击球时间为0.05s，假设速度方向均为水平方向，求：击球过程中排球的加速度。
答案
解：设排球的初速度方向为正，则由加速度定义得a=
m/s2=-600 m/s2，即加速度的大小为600 m/s2，方向与初速度方向相反
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在排球比赛中，扣球手抓住一次机会打了一个“探头球”，已知来球速度为10 m/s，击回的球速度大小为20 m/s，击球时间为0.05s，假设速度方向均为水平方向，求：击球过程中排球的加速度。
解：设排球的初速度方向为正，则由加速度定义得a=m/s2=-600 m/s2，即加速度的大小为600 m/s2，方向与初速度方向相反
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| Children find meanings in their old family tales. When Stephen Guyer's three children were growing up, he told them stories about bow his grandfather, a banker, 1 all in the 1930s, but did not lose sight of what he valued most. In one of the darkest times 2 his strong-minded grandfather was nearly 3 , he loaded his family into the car and 4 them to see family members in Canada with a 5 , "there are more important things in life than money." The 6 took on a new meaning recently when Mr. Guyer downsized to a 7 house from a more expensive and comfortable one. He was 8 that his children, a daughter, 15, and twins, 22, would be upset. To his surprise, they weren't 9 , their reaction echoed (共鸣) their great-grandfather's. What they 10 was how warm the people were in the house and how 11 of their heart was accessible. Many parents are finding family stories have surprising power to help children 12 hard times. Storytelling expects say the phenomenon reflects a growing 13 in telling tales, evidenced by a rise in a storytelling events and festivals. A university 14 of 65 families with children aged from 14 to 16 found kids' ability to 15 parents' stories was linked to a lower rate of anger and anxiety. The 16 is telling the stories in a way children can 17 . We're not talking here about the kind of story that 18 , "When I was a kid, I walked to school every day uphill both ways, barefoot in the snow." Instead, we should choose a story suited to the child's 19 , and make eye contact (接触) to create "a personal experience". We don't have to tell children 20 they should take from the story and what the moral is. | ||||
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