Cart is set rolling across a level table, at the same speed on every trial. if it runs into a patch of sand, the cart exerts on the sand an average horizontal force of 6 n and travels a distance of 6 cm through the sand as it comes to a stop. if instead the cart runs into a patch of flour, it rolls an average of 18 cm before stopping. what is the average magnitude of the horizontal force the cart exerts on the flour? 2 n