Aparticle of mass m scatters off a second particle with mass m according to a potential:
u(r) = α / r^2 , α > 0
initially m has a velocity v0 and approaches m with an impact parameter b. assume m < < m, so that m can be considered to remain at rest during the collision.
1. find the distance of closest approach of m to m.
2. find the laboratory scattering angle. (remember that m remains at rest.)

You have two photos of a person walking. one shows the person at the corner of third and main streets, the other shows the person at the corner of tenth and main streets. there are lampposts at every corner in this town, and the first picture shows it to be 10: 32: 00 exactly. the second picture shows it to be 10: 49: 30. you know three facts: (1) all of the clocks are synchronized; (2) there are exactly 12 equal-sized blocks per kilometer in this town; and (3) the streets that cross main in this area are numbered consecutively, with no interruptions. what is the person’s average speed in kilometers per hour?