A truck carries a rectangular container partly filled with water.
a) Initially, the truck travels on a horizontal road with a constant speed. Sketch the free surface of the water.
b) At some location, the road points downhill with a constant slope. Is it possible for the driver to maintain a horizontal free surface of the water? If so, what type of motion should he try to impose on the truck?
c) While on the same road as in b), is it possible for the driver to maintain a free surface of the water that is parallel to the surface of the road? If so, what type of motion should he try to impose on the truck? Can this motion persist indefinitely? First, justify your answer verbally, then try to formulate this problem mathematically and give a quantitative answer, as time permits.

Contributed by Stavros Tavoularis, Department of Mechanical Engineering, University of Ottawa, Ottawa, Canada.Image from airport-technology.com.