Question

A balloon filled with hydrogen gas is carried from earth to moon. Then the balloon will:
A. Neither fall nor rise
B. Fall with acceleration less than g
C. Fall with acceleration g
D. Rise with acceleration g

Answer 1

Hint: In this question, we need to comment on the motion of the balloon filled with hydrogen gas and is carried from the earth to the moon. For this, we will use the concept that the gravity on the moon is one-sixth that of earth’s gravity.

Complete step by step answer:
Let the mass on the balloon be m
It is said that the balloon is initially carried from earth’s surface so a gravity g will act on the balloon and a force due to gravity will be acting downwards. Since the balloon has some air in so due to atmospheric pressure, a buoyant force acts on the balloon as shown in the diagram below.

So the acceleration in the balloon will be equal to \[a = \dfrac{{mg - {F_B}}}{m} - - (i)\]
Now it is said that the balloon rises up to the moon and as we know that there is no environment present on the moon so there will be no atmospheric pressure acting on the balloon so there will be no buoyant force acting on the balloon and since gravity on the moon is one-sixth that of earth’s gravity as shown in the diagram.

Now since no buyout force is acting on the balloon, hence we can say the balloon will fall with acceleration less than g.

So, the correct answer is “Option B”.

Note:
Students must note that whenever an object or the balloon is descending a buyout force acts on the balloon in the upward direction and when the balloon rises up then the buyout force acts in the upward direction.