Your friend has asked you to help move a 60 inch ×78 inch mattress with a mass of 75 lb_m. The two of you position it horizontally in an open flat-bed trailer that you hitch to your car. There is nothing available to tie the mattress to the trailer, but you know there is a risk of the mattress being lifted from the trailer by the air flowing over it and perform the following calculations: 

(a) Although the conditions do not exactly match those for which the Bernoulli equation is applicable, use the equation to get a rough estimate of how fast you can drive (miles/h) before the mattress is lifted. Assume the velocity of air above the mattress equals the velocity of the car, the pressure difference between the top and bottom of the mattress equals the weight of the mattress divided by the mattress cross-sectional area, and air has a constant density of 0:075 lb_m/ft³. What is your result? 

(b) You see that your friend also has several boxes of books. Since you would like to drive at 60 miles per hour, what weight of books (lbf) do you need to put on the mattress to hold it in place?