Two blocks with mass M and mass 3M that are sitting on a frictionless horizontal

Question

Two blocks with mass M and mass 3M that are sitting on a frictionless horizontal surface, are pushed together and compress a spring that is mounted horinzontally between them. The spring remains in place because the compression leads to a sufficuent amount of friction with the slide wallls of the blocks. It is important to understand that the spring is NOT atached to the blocks, in other words, the spring falls down as soon as the distance between the blocks exceeds the natural length of the spring. After the blocks are pushed together, a horizontal rope then secures the blocks in place. Later the rope is cut with scissors, and the heavier blocks is observed to be launched with a speed of 2 m/s is the positive x-direction.

Define the system and the interaction of interest (be careful not to overlook aby forces!), and justify very precisely the principle(s) you apply to calculate the launching speed of the lighter block. In other words, do not just give an equation and the numerical answer, but explain with all the necesary detail why you are allowed to use this equation.

USE IMPULSE-MOMENTUM APPROACH ONLY.

Explanation / Answer

Momentum is conserved which originally was 0 so the momentum in the positive directio must equal the momentum in the negative direction.

3M*2= M*x

x= 6m/s speed of smaller block.

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