Serway & Jewett — Linear Momentum and Collisions: Problem 5

Two blocks of masses \( m \) and \( 3m \) are placed on a frictionless, horizontal surface. A light spring is attached to the more massive block, and the blocks are pushed together with the spring between them (Fig. P9.5). 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 \( 2.00 \text{ m/s} \). (a) What is the velocity of the block of mass \( m \)? (b) Find the system’s original elastic potential energy, taking \( m = 0.350 \text{ kg} \). (c) Is the original energy in the spring or in the cord? (d) Explain your answer to part (c). (e) Is the momentum of the system conserved in the bursting-apart process? Explain how that is possible considering (f) there are large forces acting and (g) there is no motion beforehand and plenty of motion afterward?