A body of mass 40kg, moving at 12m/s, collides with a stationary body of mass 20kg. The 40kg body comes to an immediate stop and the 20kg body starts to move. At what speed will the 20kg move?

Amichelson interferometer operating at a 600 nm wavelength has a 3.02-cm-long glass cell in one arm. to begin, the air is pumped out of the cell and mirror m2 is adjusted to produce a bright spot at the center of the interference pattern. then a valve is opened and air is slowly admitted into the cell. the index of refraction of air at 1.00 atm pressure is 1.00028.how many bright-dark-bright fringe shifts are observed as the cell fills with air?