Explain why theories may be changed or replaced overnight time.

Sort the images based on whether there's a force of attraction or repulsion between the magnets shown. attraction repulsion

Complete these sentences. if a roller coaster train has a potential energy of 1,500 j and a kinetic energy of 500 j as it starts to travel downhill, its total energy isj. once the roller coaster train gets closer to the bottom of the hill, its kinetic energy increases to 1,100 j, and its potential energy decreases to j. when the train reaches the bottom of the track and is traveling along the ground, its kinetic energy isj.

When doing scientific research ,the sources used should be ?