An atom of beryllium (m = 8.00 u) splits into two atoms of helium (m = 4.00 u) with the release of 92.2 kev of energy. suppose the beryllium atom moved in the positive x direction and had a kinetic energy of 38.7 kev. one of the helium atoms is found to be moving in the positive x direction. find the direction of motion of the second helium, and find the velocity of each of the two helium atoms. solve this problem in two different ways: by direct application of conservation of momentum and energy; and by applying the results if the original beryllium atom is at rest to a frame of reference moving with the original beryllium atom and then switching to the reference frame in which the beryllium is moving.

Areaction involves burning. this reaction requires energy to start, but it releases more energy than is required to start it. oxygen is always a reactant, and the products are usually carbon dioxide and water. a reaction occurs when a compound breaks down. this reaction has one reactant and two or more products. energy, as from a battery, is usually needed to break the compound apart. a reaction occurs when two substances combine to form one substance. an example of this kind of reaction is rusting, in which iron reacts with oxygen. a reaction that involves the replacement of atoms is a reaction. an atom from one reactant replaces an atom in the other reactant. this kind of reaction has two reactants and two products. an example is the neutralization of an acid and an alkali.