题目

When I was a teenager, we were the only family in our New York town that didn’t own a car. And having no car was ___21___ because all my friends’ parents did. We were poor. Suddenly a moment arrived ___22___ my life forever. For weeks a new Buick Road Master ___23___ in the window of the biggest store on Main Street. Now, on the special night, I stayed in the shadows at the edge of the crowd waiting for the winning ___24___to be drawn. It had never even entered my mind that we would ___25___. But the loudspeaker called my father's name! ___26___ I wormed my way up to the platform, 如图，水平地面上，质量为4m的凹槽左端紧靠墙壁但不粘连；凹槽内质量为m的木块压缩轻质弹簧后用细线固定，整个装置处于静止状态．现烧断细线，木块被弹簧弹出后与凹槽碰撞并粘在一起向右运动．测得凹槽在地面上移动的距离为s．设凹槽内表面光滑，凹槽与地面的动摩擦因数为μ，重力加速度为g，求：（1）木块与凹槽碰撞后瞬间的共同速度大小v；（2）弹簧对木块做的功W．