题目

质量为m的小物块，用轻弹簧固定在光滑的斜面体上，斜面的倾角为α，如图所示。使小物块和斜面体一起由静止开始向右做加速运动，加速度从零逐渐缓慢增大，已知轻弹簧的劲度系数为k，重力加速度用g表示。求：    （1）加速度为零时，弹簧的伸长量？    （2）小物块对斜面体的压力为零时，斜面体向右的加速度？  阅读短文，判断正误，用“正确”或“错误”表示。Little Jack is playing with his friend near a bank. A man stops beside them. The dooropens and a man gets out. He is wearing a mask. There's a gun in his hand. LittleJack's friend is frightened. But Jack is not. He runs to a policeman. "Please comequickly," Jack says. "A robber（强盗） is in that bank." The policeman looks at the bank andlaughs. "Oh, good boy！" the policeman says. "But it's Ok. That man is not a robber.He's an actor.（演员）"（1）Jack is in the bank with his friend.（2）Jack sees a man with a gun.（3）Jack is frightened.（4）Jack and his friend telephone the police.（5）The man with a gun isn't a robber.