5. Two objects, X and Y, are held at rest on a horizontal frictionless surface and a spring is compressed between them. The mass of X is 5/2 times the mass of Y. Immediately after the spring is released, X has a kinetic energy of 50 J and Y has a kinetic energy of:
(A) 20 J
(B) 8 J
(C) 310 J
(D) 125 J
(E) 50 J
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