Please Listen to the following TED talk and answer the questions followed. (1分11秒-55秒) What happened when the speaker just built the instrument with his team to propose an experiment to fly to Venus?
A.
He just joined NASA
B.
He became involved in calculations of the greenhouse effect on earth and found that our atmospheric composition was changing
C.
He has just resigned as principal investigator on the Venus experiment
D.
He was continuing his experiment on the trip to Venus
【简答题】如图所示,光滑平行导轨倾斜放置,导轨平面倾角为 θ =30° ,导轨间距为 L ,导轨上端接有阻值为 R 的定值电阻,整个装置处在垂直导轨平面向上的匀强磁场中,磁场的磁感应强度大小为 B ,一根金属棒放在导轨上,由静止释放,同时给金属棒施加一个沿导轨平面向下的拉力,使金属棒以大小为 a =0.5g 的加速度向下做匀加速运动, g 为,金属棒运动过程中始终与导轨垂直并接触良好,不计导轨和金...