... C.物体 B 对斜面的作用力减小 D.地面受到的摩擦力大小可能变大 21.如图所示是导轨式电磁炮的原理结构示意图。两根平行长直金属导轨沿水平方向固定, 其间安放炮弹。炮弹可沿导轨无摩擦滑行,且始终与导轨保持良好接触。内阻为 r 可控 电源提供的强大恒定电流从一根导轨流入,经过炮弹,再从另一导轨流回电源,炮弹被 导轨中的电流形成的磁场推动而发射。在发射过程中,该磁场在炮弹所在位置始终可以 简化为磁感应强度为 B ...
... Named the “Father of Traffic Safety,” Eno developed the first traffic plans for major cities including New York, London, and Paris, and is credited with helping to invent and popularize [r] ...
... The refrigerator takes photos of what’s inside every time the door is shut, (17) so users always know how much food is left and what needs to be purchased at the store. Users can access[r] ...