A 1/4 scale model of a tractor trailer is tested in a wind tunnel under standard sea level conditions. The model frontal area is 6.75 ft^2 . Determine the air speed at which the model should be tested to ensure dynamically similar results if the highway speed of the prototype rig is 55mph. When tested at this airspeed, the measured drag force is 784lb. What is the drag coefficient of the model? Also calculate the Drag force on a prototype tractor trailer at a highway speed of 55 mph.