题目

阅读下列短文，从每题所给的A、B、C和D项中，选出最佳选项，并在答题卡上将该项涂黑。 An independent college claimed to have become the first school in England to make Chinese a compulsory (强制的) subject for its pupils.  Richard Cairns, the headmaster of Brighton College, said the move aims to recognize the importance of China as the world’s fastest growing economy.     Chinese will become one of the core subjects at the 1,200-pupil college from September. At present the school has only a “handful” of native Chinese students, but it hopes to at卢瑟福用α粒子轰击氮核发现质子。发现质子的核反应为：。已知氮核质量为mN=14.00753u，氧核的质量为mO=17.00454u，氦核质量mHe=4.00387u，质子(氢核)质量为mp=1.00815u。(已知：1uc2=931MeV，结果保留2位有效数字)求：（1）这一核反应是吸收能量还是放出能量的反应？相应的能量变化为多少？（2）若入射氦核以v0=3×107m/s的速度沿两核中心连线方向轰击静止氮核。反应生成的氧核和质子同方向运动，且速度大小之比为1:50。求氧核的速度大小。