When air is heated it... 1 point rises because its density increases rises because its density decreases falls because it density decreases falls because it density increases

Can someone explain to me how to do this problem ?

What is the momentum of a 2 kg object moving at 15 meters per second

Examine the equation. 23490th→23088ra+42he what kind of barrier would you need to block the radioactive particles from this reaction? a.a piece of paper b.a sheet of aluminum foil c. a two-inch block of lead d. a solid concrete block