Which two forms of electromagnetic energy are used to produce the most spectacular fluorescence when placed in darkness?
1. microwaves and x rays
2. microwaves and infrared
3. ultraviolet and x rays
4. ultraviolet and infrared

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.