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## Homework Statement

A 500g putty ball moving horizontally at 6m/s collides with and sticks to a block lying on a friction-less horizontal surface. If 25% of the kinetic energy is lost, what is the mass of the block?

## Homework Equations

initial (i) = final (f)

m1v1+m2v2 = m1v1+m2v2

## The Attempt at a Solution

(m1v1i - m1v1f ) /v2f I'm confused :-( Somebody help me solve this. Also is the reduction of the kinetic energy relevant to solving this question?