Answer:
When you push your younger sister on a swing in a park, several things are happening in terms of the second and third laws of motion.
First, let's consider the initial push you give your sister. According to the second law of motion, this push will cause your sister to experience an acceleration in the direction of the force you applied. The magnitude of this acceleration will be proportional to the force applied and inversely proportional to the mass of your sister, as described by the equation F = ma. The direction of the acceleration will be in the direction of the force you applied, which is in the direction of the swing.
Now let's consider the harder push you give your sister. According to the third law of motion, for every action, there is an equal and opposite reaction. This means that the force you applied to your sister in the direction of the swing will cause an equal and opposite force to be applied to you in the opposite direction. As a result, you will also experience an acceleration in the opposite direction, away from the swing.
At the same time, your sister will experience an acceleration in the direction of the force you applied, which will cause her to swing higher and faster. The magnitude of this acceleration will again be proportional to the force applied and inversely proportional to your sister's mass. However, because your sister is now swinging faster, the force of air resistance will also increase, which will eventually cause her to slow down and come to a stop.