Linear momentum has to be conserved. It was zero before the thread eas burned ... when nothing was moving ... so the momentum of the masses moving in opposite directions has to add up to zero. ... Momentum = mass times speed. ... In one direction, you have 5 kg times 1/5 m/s= 1 kg-m/s. ... We need 1 kg-m/s in the other direction. ... 7 kg times speed = 1 kg-m/s. ... Can you finish it from here ?
The answer would be 1/7 m/s because the initial momentum in the objects is 0, then the final momentum of the objects must be 0. if the 5 kg object has a momentum of 1 (5 * 1/5) then the other object must be -1. The only velocity that will produce that result is -1/7 m/s, but since speed doesnt take into account the direction of an object.
The correct answer is matter. Matter is a physical substance, so it is that only option provided that can be broken down to the subatomic particle level.
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