Does the more cars on a roller coaster going down hill make it travel farther?

The number of cars on a roller coaster does not affect how far it travels down a hill. The potential energy stored in the roller coaster at the top of the hill is converted into kinetic energy as it rolls down the hill. This kinetic energy is then dissipated as the roller coaster climbs the next hill or as it experiences friction from the track and air. The total amount of energy available to the roller coaster is determined by the height of the hill and the mass of the roller coaster and its passengers. Adding more cars to the roller coaster increases the total mass, but it also increases the amount of friction between the roller coaster and the track, so the net effect on the roller coaster's distance traveled is negligible.