题目

质量为m,电荷量为q的带电粒子由静止开始，在电压为U的电场中仅在电场力作用下加速后的速度为___________ 答案：【答案】【解析】带电粒子经加速电场加速后，动能的大小等于电场力做功，求得速度v；设加速后的速度为v，根据动能定理可得：，所以。 The child asked his mother ________ go out to play tennis.A．that he could B．if he could C．if could he D．that could he