A horizontal force of 90.7 N is applied to a 40.5 kg crate on a rough, level surface. If the crate accelerates at 1.08 m/s, what is the magnitude of the force of kinetic friction (in N) acting on the crate?

The drag force, fd, imposed by the surrounding air on a vehicle moving with velocity v is given by fd = cdaρv 2/2 where cd is a constant called the drag coefficient, a is the projected frontal area of the vehicle, and ρ is the air density. an automobile is moving at v = 80 kilometers per hour with cd = 0.28, a = 2.3 m2, and ρ = 1.2 kg/m3.