Jera cut her finger. the next day, the skin around the cut had become red and warm. why are these signs of infection?

These happen because of an inflammatory response! It's the first reaction your body has to an infection

When the ball is rising up, it gains kinetic energy. when the ball reaches the very top, it will have all potential energy, until it falls back down and gains it kinetic energy. finally when you catch the ball or it falls back down, it would have gained its potential energy back.