题目

Life is filled with challenges. As we get older we come to realize that those challenges are the very things that __1______ us and make us who we are. It is the same with the challenges that come with __2______. When we are faced with a challenge, we usually have two __3______. We can try to beat it off, or we can decide that the thing __4______ the challenge isn’t worth the __5______ and call it quits. Although there are __6______ times when calling it quits is the right thing to do, in most __7______ all that is needed is __8______ and communication. When we are committed to somet（2012?莆田模拟）如图甲所示，一对足够长的平行光滑轨道放置在水平面上，两轨道相距L=1m，左端之间用R=3Ω的电阻连接，轨道的电阻忽略不计．一质量m=0.5kg、电阻r=1Ω的导体杆静置于两轨道上，并与两轨道垂直．整个装置处于磁感应强度B=2T的匀强磁场中，磁场方向垂直轨道平面向上．现用水平拉力沿轨道方向拉导体杆，拉力F与导体杆运动的位移x间的关系如图乙所示．当拉力达到最大时，导体杆恰好开始做匀速运动．当位移x=2.5m时撤去拉力，导体杆又滑行了一段距离△x后停下，已知在滑行△x的过程中电阻R上产生的焦耳热为12J．求：（1）拉力F作用过程中，通过电阻R上的电量q；（2）导体杆运动过程中的最大速度vm；（3）拉力F作用过程中，回路中产生的焦耳热Q．