6. A truck runs into a pile of sand, moving 0.80 m as it slows to a stop. The magnitude of the work that the sand does on the
truck is 6.0 X 10^5J. (a) Determine the average force that the
sand exerts on the truck. (b) Did the sand do positive or nega-
tive work? (c) How does the average force change if the stop-
ping distance is doubled? Indicate any assumptions you made.