a) The original energy is in the cord. The cord is holding the blocks together, so the energy is stored in the tension of the cord.
b) Momentum is conserved in the bursting-apart process. The large forces acting on the blocks cause them to accelerate, which results in a change in momentum. However, the total momentum of the system remains the same since the blocks move in opposite directions with equal and opposite velocities.
Two blocks of masses M and 3M are placed on a horizontal, frictionless surface. A light spring is attached to one of them, and the blocks are pushed together with the spring between them as shown in the figure below. A cord initially holding the blocks together is burned; after that happens, the block of mass 3M moves to the right with a speed of 1.85 m/s.
(a) Is the original energy in the spring or in the cord? Explain your asnwer.
(b) Is momentum of the system conserved in the bursting-apart process? How can it be, with large forces acting? How can it be, with no motion beforehand and plenty of motion afterward?
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