**Answer:**

The system's kinetic energy changes by 3.6 J

**Explanation:**

The given parameters are;

The number of cart = 2

The mass of each cart = 0.5kg

The initial length of the spring = 0.50 m

The final length of the spring =T0.3 m

The change in position of the first cart = 0.6 m

The energy given to the first cart = Work done by the force = Force × Displacement

The initial kinetic energy of the two cart moving together = Energy given to the first cart = 6.0 × 0.2 = 1.2J

The kinetic energy given to the two cart combined = The applied force × The total displacement of the two cart as they move together

The kinetic energy given to the two cart combined = 6.0 × (0.6 - 0.2)

The kinetic energy given to the two cart combined = 6.0 × 0.4 = 2.4 J

The total kinetic energy given to the two cart = 1.2 + 2.4 = 3.6 J

The total kinetic energy given to the two cart = 3.6 J

The system's kinetic energy changes by 3.6 J.

The answer is A. Opposite charges attract; like charges repel.

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The correct option is B.

The length of an object, the mass of an object and the rate of time passage for an object can change depending on the situation which the object is subject to. For instance in space, the mass and the velocity of an object usually change. But, the value of the speed of light in the space is the same for all observers regardless of the motion of an object, that is, the speed of light is a constant.<span />