Ball hitting block, elastic collision

[geauxKTM]

Homework Statement

.500kg ball attached to a cord that is 70 cm long. ball strikes a 2.5kg block at rest

what is the speed of the ball just before hitting the block
and collison is perfectly elastic find speed of ball and block after collision

Homework Equations

The Attempt at a Solution

Uo=MGY
(.5)(9.8)(.7)= 3.43J
Ko=0
Uf=0
J=.5(.5)v^2= 2.62

part b
2.62=V2f-V1f
1.31=.5V1f+2.5V2f

matrix on calc
V1f= -1.75
V2f=.87

 

[ideasrule]

I don't understand the question. Do you have a diagram? How is the cord attached? Is it a spring or something?