You are out and about in the country and your father sees a rock that he really wants in the yard. now you must get the very heavy rock into the back of a truck. the truck bed is 3 feet off the ground. your father pulls out a 5-foot plank and begins to set up a ramp. at the same time, you (who know about mechanical advantage! ) have found a plank that is 8 feet long, and you show it to your father. which plank will give you the most mechanical advantage? calculate the ma for each plank