Diver uses a sonar device to determine the distance to her diving partner. the device sends a sound wave and records the time it takes for the wave to reach the diving partner and return to the device. suppose the wave travels at a rate of about 4000 feet per second. the wave returns 0.8 second(s) after it was sent. how far away is the diving partner?

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?