Two identical cars are at the top of a hill, one has a driver and three passengers, the other just the driver. Both drivers release the hand break at the same time, which would reach the bottom first. I have used two cars as the example as this will reduce the possible variables such as wind resistance; in this example every condition is the same for both cars other than the weight. I believe they would reach the bottom at the same time as the only force acting on them is gravity. I am far from being an expert but seem to remember this from my days at college, my colleague argues that the heavier car will reach the bottom first due to momentum gains, please could someone put us out of our misery?