Collision problem, and I can't figure out how they got this answer.
You have been asked to design a 'ballistic spring system' to measure the speed of bullets. A bullet of mass m1 is fired into a bullet of mass M2. The block, with the embedded bullet, then slides across a frictionless table and collides with a horizontal spring whose spring constant is k. The opposite end of the spring is anchored to a wall. The spring's maximum compression d is measured.
Find an expression for the bullet's speed VB in terms of m1, M2, k, and d.
The back of the book says
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