Read and write.

1. A: Did you _                             ?

    B: Yes, I did.

2. A:  Did you                               ?

    B: Yes,                                        .

3. A:                                    ?

    B: No,                                        .

4. A:                                       ?

    B: No,                                       .

5. A:                                   ?

    B: No,                                 .

用一个弹簧玩具枪将子弹竖直弹射向上，发射前弹簧的弹性势能为18J，如果发射后其势能全部转化为动能，当子弹上升到6m时，其动能变为5J，则子弹在6m处的重力势能为多大？子弹最多可上升到多高？（整个过程子弹机械能守恒）