题目

劲度系数为k、长为L的轻弹簧上端固定,下端系一质量为m的小球,小球可在竖直方向上做简谐运动.它的回复力由_______________提供,平衡位置处弹簧长度为_______________. 答案：弹力和重力的合力      L+解析：在竖直方向做简谐运动的小球,它的回复力由重力和弹力的合力提供,平衡位置F回=0,即kx=mg,x=,所以l=L+.—Can you tell me__ __?— He is kind and generous. He always helps others.A. what your buddy likesB. what your buddy is likeC. what does your buddy look likeD. what does your buddy like