Heavy water has a chemical formula d_2o. it is a form of water in which all hydrogen is deuterium ^2h and has a density of 1.11 g/cm^3. neglect the contribution of oxygen atoms. calculate the number of collisions required to slow down a neutron from 2 mev to 0.025 ev heavy water. determine the diffusion length of thermal neutrons in heavy water.

Two cannon balls weighing 18 kg and 24 kg are chained together and fired horizontally with a velocity of 165 m/s from the top of a 21-m wall. the chain breaks during the flight of the cannonballs and the 18-kg cannonball strikes the ground at t = 1.5 s, at a distance of 240 m from the foot of the wall, and 7 m to the right of the line of fire. determine the position of the other cannonball at that instant. neglect the resistance of the air.