A car traveling at a rate of 30 ft/sec is approaching an intersection. When the car is 120 ft from the intersection, a truck traveling at a rate of 40 ft/sec crosses the intersection. If the roads are at right angles to each other, how fast are the car and the truck separating 2 seconds after the truck crosses the intersection?

.If a ladder of length 30 ft that is leaning against a wall has its upper end sliding down the wall at a rate of 1/2 ft/sec, what is the rate of change of the acute angle made by the ladder with the ground when the upper end is 18 ft above the ground?