题目

Mrs. Smith is Jim's mother. She loves her family very much. She goes to the store every day. She often buys food, fruit and clothes for Jim and her husband（丈夫）. Now many clothes are on sale at Renmin Clothes Store. They are very cheap. Mrs. Smith comes to the store and she wants to buy some clothes for her family. There they have sweaters in all colors for ￥15 each and sports shoes for only ￥28. Mrs Smith likes the red sweater and she buys one for herself. She buys a pair of sports shoes for her son. The great T-shirts in the store are just ￥18! She buys a white one for Mr Smit（2013?湖北模拟）如图甲所示，真空室中电极K发出的电子（初速度不计）经过电势差为UΘ的加速电场加速后，沿两水平金属板C、D间的中心线射入两板间的偏转电场，最后打在荧光屏上．C、D两板间的电势差UCD随时间变化的图象如图乙所示，设C、D间的电场可看作匀强电场，且两板外无电场．已知电子的质量为m、电荷量为e（重力不计），C、D极板长为l，板间距离为d，偏转电压UΡ，荧光屏距C、D右端的距离为16，所有电子都能通过偏转电极．（1）求电子通过偏转电场的时间t0；（2）若UCD的周期T=t0，求荧光屏上电子能够到达的区域的长度；（3）若UCD的周期T=2t0，求到达荧光屏上O点的电子的动能．