identical particles are placed at the 50-cm and 80-cm marks on ameter stick of neglibile mass. this ridigd body is then mounted so as to rotate freely about a pivot at hte 0 cm mark on the meter stick. if this body is released from rest in a horizontal position, what is the angular pseed of hte meter stick as it swings through it's lowest position

An alpha particle with kinetic energy 12.5 mev makes a collision with lead nucleus, but it is not "aimed" at the center of the lead nucleus, and has an initial nonzero angular momentum (with respect to the stationary lead nucleus) of magnitude l = p0 b, where p0 is the magnitude of the initial momentum of the alpha particle and b=1.40×10−12 m. (assume that the lead nucleus remains stationary and that it may be treated as a point charge. the atomic number of lead is 82. the alpha particle is a helium nucleus, with atomic number 2.) what is the distance of closest approach?