So suppose two carts roll down a hill. One is more massive than the other, but they both have the same size. Neglecting air resistance, which one reaches the bottom first? Without friction, I think both reach the bottom at the same time. However my first thought was that the heavier car will have a greater friction force, the lighter one will reach the bottom first. However, I'm not sure if the mass cancels from all the friction terms. Any insight?