Wow ! This is not simple. At first, it looks like there's not enough information, because we don't know the mass of the cars. But I"m pretty sure it turns out that we don't need to know it.
At the top of the first hill, the car's potential energy is
PE = (mass) x (gravity) x (height) .
At the bottom, the car's kinetic energy is
KE = (1/2) (mass) (speed²) .
You said that the car's speed is 70 m/s at the bottom of the hill, and you also said that 10% of the energy will be lost on the way down. So now, here comes the big jump. Put a comment under my answer if you don't see where I got this equation:
(There goes the mass. As long as the whole thing is 90% efficient, the solution will be the same for any number of cars, loaded with any number of passengers.)
Answer:It increases confidence because the more times you conduct the same experiment over and over should either prove your hypothesis right and wrong and eliminate any random occurrences that might affect your results.
