作业帮7.As shown above,a ball of mass m,suspended on the end of a wire,is released from height h and collideselastically,when it is at its lowest point,with a block of mass 2m at rest ona frictionless surface.After the collision,the ball rises to a final h
来源：学生作业帮助网 编辑：作业帮 时间：2024/11/17 12:20:54
7.As shown above,a ball of mass m,suspended on the end of a wire,is released from height h and collideselastically,when it is at its lowest point,with a block of mass 2m at rest ona frictionless surface.After the collision,the ball rises to a final h
7.As shown above,a ball of mass m,suspended on the end of a wire,is released from height h and collideselastically,when it is at its lowest point,with a block of mass 2m at rest ona frictionless surface.After the collision,the ball rises to a final heightequal to
(A) 1/9h
(B) 1/8h
(C) 1/3h
(D) 1/2h
(E) 2/3h
如果用能量守恒,和动量守恒做的话,mv=mv1+2mv2 1/2mv1^2+1/2mv2^2=mgh=1/2mv^2
得出v1=3/5根号2gh 方向左 v2=4/5根号2gh 方向有 相对速度由原来的v变成了 7/5v 哪里做错了
7.As shown above,a ball of mass m,suspended on the end of a wire,is released from height h and collideselastically,when it is at its lowest point,with a block of mass 2m at rest ona frictionless surface.After the collision,the ball rises to a final h
mv=mv1+2mv2 正确
1/2mv1^2+1/2mv2^2=mgh=1/2mv^2 错误,应该是：
1/2mv1^2+1/2(2m)v2^2=mgh
解出的一组解将是v1=√(2gh) v2=0 应略去,另一组解是有效解,且v1一定是负值.
.不必求出v的具体数值。