Two Blocks Are at Rest on a Horizontal Frictionless Surface

Multiple Choice

Two blocks are at rest on a horizontal frictionless surface with a compressed spring between them.The 15.0-kg block accelerates when the string holding the system in compression is cut and the 30.0-kg box accelerates in the opposite direction.What is the magnitude of the force from the expanding spring on the 30.0-kg box when the 15.0-kg box is undergoing an acceleration of 5.00 m/s²?

A) 37.5 N
B) 150 N
C) 225 N
D) 75.0 N
E) 0 N