Final answer:
The situation described violates the conservation of momentum because in an elastic collision within a closed system, both momentum and kinetic energy should be conserved. One ball leaving with twice the speed and the same mass does not provide an equal exchange of momentum, despite energy potentially being conserved if converted correctly.
Step-by-step explanation:
The toy described is an example of elastic collisions in one dimension, where kinetic energy and momentum are conserved. In the scenario where two balls are elevated and released to slam into the aligned row of balls, the expected outcome is for two balls to pop out the other side with a velocity equal to that of the released balls in an ideal, frictionless system. If instead of two balls, one ball were to pop out with twice the speed, this would indicate a violation of the conservation of momentum, but not necessarily energy, mass, or velocity. In elastic collisions, the total momentum and kinetic energy of the system should remain constant. An object moving with twice the speed would have four times the kinetic energy (since kinetic energy is proportional to the square of the velocity), assuming no external forces are acting on the system. If only one ball pops out on the other end, the total kinetic energy can remain constant if the speed of that ball properly compensates for the energy carried by two balls. Therefore, the conservation of energy might still be upheld if kinetic energy is converted correctly. However, the scenario most definitively violates the conservation of momentum because momentum depends on both mass and velocity, and if only one ball exits with twice the velocity, there isn't an equivalent momentum exchange.