39. A balloon filled with helium rises in air because A.Air exerts an upward force on the balloon B.The balloon is weightless C.Helium is less dense than air D.Helium pushes down on the air below the balloon
Answer: Option C Solution: In the beginning the balloon filled with helium rieses in air because weight of the air displaced by balloon is more than the weight of the balloon and helium gas filled inside balloon. We know that the density of air and the value of acceleration due to gravity decreases with height.
