The collision cross section s represents the effective target area "seen" by the asteroid and is found by multiplying (bmax)2 by π. if the asteroid comes into this area, it is guaranteed to collide with the earth. a simple representation of the cross section is obtained when we write v in terms of ve, the escape speed from the surface of the earth. first, find an expression for ve, and let v=cve, where c is a constant of proportionality. then combine this with your result for (bmax)2 to write a simple-looking expression for s in terms of r and c.